Septic tank tees:

This article describes the methods of septic tank baffle repair by the installation of replacement septic tank inlet and outlet tees.

A septic tank replacement "Tee" is simply a standard plastic pipe in the shape of a "Tee", typically 4" or 6" in diameter, that is inserted at the septic tank inlet or outlet to serve the function of the original septic tank baffle that may have been damaged or lost.

Sizing and Installing Septic Tank Tees

This article explains the requirements for septic tank inlet tees and septic tank outlet tees and explains why the length of the tee extensions is important to prevent septic tank or septic piping clogging and to protect the life of a drainfield.

Links to related septic system testing and design information are given. We address septic waste line tee sizing and we include tank tee installation suggestions.

Discussed: What Are Septic Tank Baffles or Tees? Inlet Baffle Inspection & Outlet Baffle Inspection - Effects of septic tank tee loss or septic tank baffle damage on the septic drainfield life.

Signs of Septic Tank Baffle/Tee Trouble. Septic Tank Outlet Filter Add-on. Septic tank outlet baffle or tee is installed deeper into the septic tank than the inlet tee. Septic tanks installed backwards - with outlet opening higher than inlet opening cause sewage clogs and trouble.

We also recommend septic tank outlet filters installed at the tank outlet tee to extend the drainfield life. When repairing or installing a septic tank baffle or tee, to extend drainfield life

see USING SEPTIC FILTERS.

What is a Septic Tank Tee or Baffle or Gas Baffle?

Septic tanks may come with a baffle to prevent scum from clogging the inlet or outlet piping and septic fields. In some designs the septic tank inlet baffle or tee also reduces the movement of sewer gases out of the tank and up into the building through an un-trapped sewer pipe.

The septic tank baffle or tee is a device on the inlet or outlet of a septic tank which prevents sewage back-flow into the inlet or outlet pipe.

The device may be made of concrete, steel, plastic, or other materials, but in all cases the septic tank tee or baffle forms a barrier between the septic tank and the inlet or outlet pipes to or from the septic tank.

Often the baffle is insufficient in design, and on steel septic tanks the baffle may rust off, leading to blocked septic systems and septic field failure.

A common repair or improvement is to install plastic pipe septic tees in the septic tank to perform the function of these baffles.

In the septic tank photo you can see the green PVC sewer line entering the tank at left, and at right you can see black sewage debris atop the concrete septic tank baffle.

This indicates a septic tank problem, probably at the outlet, discussed

at SEPTIC TANK BAFFLES.

Septic tank inlet baffle inspection

Where a replacement PVC plastic septic tank tee is installed into a steel or concrete septic tank, the outlet or inlet tee is a standard pipe tee, typically of the same diameter as the incoming sewer line, placed at the inlet of a septic tank to prevent the inlet sewer line from being clogged by floating scum and waste in the tank (resulting in a blocked septic system).

On the inlet side the septic tank baffle is intended to permit waste to enter the tank, but to avoid clogging of the tank inlet. The septic tank inlet baffle accomplishes this job by blocking the floating scum layer, a thick layer of debris that forms naturally at the top of a working septic tank, from blocking the tank inlet pipe.

At SEPTIC TANK BAFFLES we describe inspecting the condition of the septic tank baffles when the tank access ports have been opened, for example when the septic tank is about to be pumped.

The septic tank inlet baffle also reduces the movement of gases from the septic tank backwards into the building that it serves. Any gases that do escape the tank in this direction should be venting above the building's roof through its plumbing vent system, provided that system is itself correctly installed.

Septic tank outlet baffle (gas baffle) inspection

The septic tank outlet tee blocks floating scum and sewage from flowing out of the tank where it would rapidly clog the drain field and effluent piping.

Located on the septic tank's outlet end where the tank is connected to piping intended to conduct clarified septic effluent to the absorption system (drainfield), the septic tank baffle or tee, also called a Gas Baffle in some literature or regulations, keeps solid waste and gas bubbles away from the septic tank outlet, thereby reducing the carry over of solid particles from the septic tank.

This job is critical since sending solid waste out of the septic tank into the drainfield (absorption area) will certainly lead to clogging of the soils there, shortening the life of the drainfield. We describe this septic tank baffle or tee inspection in more detail

at SEPTIC TANK BAFFLES.

Signs of Trouble With Septic Tank Baffles or Tees

Watch out: the most-serious problems that can occur if the septic tank baffles or tees are damaged, missing, are at the wrong height, or are improperly-installed include

• a sewage backup in the building
• a failed drainfield or soakaway bed caused by pushing solid waste out of the septic tank into the effluent absorption system

Replacement Septic Tank Tee or Baffle Procedure & Specifications

If the SEPTIC TANK BAFFLES have been damaged, lost, or are inadequate, a septic tee should be installed at both the tank inlet [photo] and outlet [photo] .

Our photo , compliments of architect Jerry Waters, [reference] shows a badly deteriorated concrete septic tank baffle.

A damaged baffle such as this one will permit floating scum and solids in the septic tank to block the septic tank inlet, leading to a sewer backup in the building. Damaged tees may also increase the movement of sewer gases back up the sewer line into the building.

While a septic tank designer could specify the exact numbers that s/he would want us to use for installing the inlet and outlet tees for a septic tank, we have not yet found such a specification.

Most installers use local "rules of thumb" for septic tank baffle design.

Perhaps this is because the inlet and outlet tee dimensions for a septic tank depend on the size and depth of the tank as well as the anticipated thickness of the floating scum layer in the septic tank.

To install a pipe tee at a septic tank inlet or outlet pipe where the original baffle has been lost, it is necessary to excavate the septic tank, remove the cover, and gain access to the inlet and outlet pipes just inside the tank near the top.

The cost of the 4" to 6" diameter plastic pipe tee will be trivial, just a few dollars each, for a total of usually less than $20.00. The cost of excavating and opening the septic tank so that the tee can be installed depends on your particular septic tank installation, the depth of the tank, and its condition.

As you can see in this photo of standard 4" PVC pipe fittings assembled to form a replacement septic tank tee to repair the tank with the damaged concrete septic tank baffle shown above, the parts are assembled into a tee with the longer extension to be inserted downwards into the septic tank.

In architect Waters' photograph of these septic tank baffle repair parts (above left), he has used a 22 degree elbow to connect the tee to the sewer line entering the septic tank.

Mr. Waters used the angled elbow rather than a straight connection on the tee to avoid bringing the top of the "tee" fitting too high in the septic tank.

You don't want the replacement tee to slope upwards nor do you want any obstruction in these fittings that could cause a blockage of sewage entering the septic tank.

The center of the plastic tee is inserted into the septic tank inlet opening just inside the tank, and the tee is installed vertically as you can see in our sketch above. If the center of your plastic tee is female rather than male, the larger hub may not fit into the septic tank inlet or outlet opening.

In that case your installer may need to glue a short length of plastic pipe into the female tee hub so that you can install this fitting. Keep the new inlet or outlet septic tank tee close to the tank wall as shown in our sketch.

Sample Specifications for a Septic Tank Inlet Tee

Mr. Waters' photograph (left) shows the new PVC septic tank tee parts in position in the septic tank. You'll notice that he had to chip away the remains of the concrete septic tank baffle to get the new plastic parts in place.

On steel septic tanks removing the remains of the steel baffle will also be necessary - don't get cut or you risk a serious infection.

What you'd want to see at the inlet is that the top of the tee clears the tank cover when it's put on and that it's clear of the top of the floating scum layer - otherwise it'll get blocked.

The bottom of the tee should be BELOW the BOTTOM of the floating scum layer when the tank is filled to its normal level.

Otherwise your incoming line is going to be blocked by the scum layer.

The inlet tee also slows the water as it flows into the tank so that you don't stir things up inappropriately.

In the informal drawings we have at hand the bottom of the inlet extends to just above the middle of the tank depth - we guess the presumption is that this clears the bottom sludge layer and the top scum layer.

 

Just as the inlet tee needs to extend below the floating scum so as not to become blocked by it, the outlet tee needs to extend 2 or 3 inches DEEPER than the bottom of the inlet tee.

This keeps sewage and floating scum from running out the tank outlet where it would quickly clog the absorption system or drainfield.

So, and let's take a typical septic tank that is maybe 5 feet of internal depth.

The inlet pipe enters the tank perhaps 6 inches below the very top edge of the tank (top edge of the tank to top edge of the inlet hole) and is about 4 inches in diameter. So the bottom of the septic tank inlet opening (and outlet opening) in our theoretical example is about 10 inches from the top of the tank.

This will define, roughly, the height top of the floating scum layer.

(Even though the scum layer is blocked from flowing out of the tank by the outlet tee, it will rise up to about the same level as the bottom of the outlet tee, or slightly above it.

Septic effluent will flow up the outlet tee from the bottom of the outlet tee up out of the septic tank, keeping the total sewage level in the tank from rising any higher.)

The bottom of the floating scum layer will vary depending on the thickness of that layer. Let's allow for an 8 inches thick floating scum layer. (A rental house septic tank which we examined recently had a 4 inch scum layer when it was pumped after 7 years of use by an average of 1 person occupancy.)

That means the bottom of the 8 inch thick floating scum layer would extend down in the tank to about 8 inches below the bottom of the tank inlet opening.

Your inlet tee had better be at least a couple of inches deeper than that or your scum layer, else the floating scum will clog and back up the septic system. So for these example dimensions I'd make my inlet tee extend down into the tank at least 12 inches below the bottom of the tank inlet at a minimum.

In the septic tee replacement parts photos shown above, Mr. Waters assembly was just under 30" in total length, including the vertical dimension of the PVC pipe tee itself.

Should we make the inlet tee bottom extension longer?

Yes.

I'd bring it to perhaps a little above the mid-depth of the waste that's going to be in the tank - putting it between the bottom of the floating scum layer and the top of any sludge on the tank bottom.

A bit longer means the tee does a bit better job of slowing the incoming wastewater down.

So I might make my inlet tee extend down 14 inches to 16 inches into the tank.

Are Septic Tank Tees Open or Shut at their Top End?

What is to be done at the top of the new septic tank tee after it's inserted into the tank inlet (or outlet) pipe? We leave the tee top open, yielding a septic tank function and design similar to that found on concrete septic tanks.

Jerry Waters' photograph of the finished septic tank replacement tee (left) shows that he installed a grate on top of the septic tank tee top opening.

The grate body needed to be trimmed down to minimize its height as the top of the tee in this installation was very close to the under-side of the septic tank cover.

Waters wanted to reduce the chances of solids flowing over the top of and clogging the septic tank inlet tee should there be a tank outlet blockage.

DO NOT install any grate or blocking device on the bottom of the septic tee extension of the system will clog very quickly.

Open septic tank tee tops have some advantages:

• Waste may flow more easily into the tank, reducing gas pressure or debris blockage at the tank inlet
• If the septic tank tee outlet bottom end becomes clogged with debris, the open tee top provides an emergency "overflow" outlet that may keep the system working without backup until it's discovered at the next septic tank pumpout.

In fact, when cleaning the septic tank we like to inspect the tank inlet and outlet baffles or tees specifically to look for evidence of sewage flowing over the top of the tee or baffle - a condition that would indicate a problem, perhaps a blockage at the tank outlet tee or baffle, a blockage in the tank outlet effluent line en route to the drainfield or distribution box, or a problem with the drainfield itself.

We describe this inspection

at SEPTIC TANK BAFFLES.

To complete the septic tank tee insertion project that replaced the damaged original concrete (or steel) septic tank baffles, make sure that all of the septic tank covers and access port covers are sound, safe, and child proof. Falling into a septic tank is likely to be fatal.

Also check that ground water or surface runoff are not entering the septic tank at the sewer pipe inlet or outlet ends of the tank and similarly that runoff is not entering the septic tank at its covers. Flooding the septic tank speeds the demise of the drainfield.

See details at SEPTIC TANK LEAK.

Finally, to maximize the septic system drainfield life, make sure the septic tank is cleaned (pumped out) on a regular schedule.

See SEPTIC TANK PUMPING SCHEDULE.

Thanks to architect Jerry Waters for contributing these septic tank tee replacement photos and for suggesting clarification on the requirement to leave the top of the septic tank tee open.

Specification for Septic Tank Inlet & Outlet Tee Elevation & Depth

Level the septic tank: The septic tank inlet tee is designed to be higher than the septic tank outlet tee. This helps assure that incoming sewage clears the baffle and enters the tank correctly, while outgoing effluent does not carry along floating solids, scum, or grease (which would clog the drainfield).

For this reason the when the septic tank itself is placed into the ground, the septic tank should be installed level. If the septic tank has settled and is no longer level it would be very difficult to re-position the tank, but it may be possible to make corrections at the tank inlet tee and outlet tee to cope with this change.

Our image of a septic tank showing the relative heights of septic tank inlet and outlet and depths of baffles or tees was adapted and significantly modified from Alaska DEC [3] [Click to enlarge any image]

Septic tank outlet tee should extend deeper into septic tank than inlet tee

The septic tank outlet tee is slightly different from that found on the inlet side of the septic tank. As you see in the sketch and in the sketch of both inlet and outlet tees in the septic tank at the top of this page, the bottom of the outlet tee (drawn in blue in the sketch) should be 2 or better 3 inches deeper into the tank than the inlet tee.[2]

That green dashed line - - - we added to the drawing is just to illustrate that the bottom end of the septic tank inlet tee is about 3-inches higher in the septic tank than the bottom end of the septic tank outlet tee at the right end of the septic tank in the sketch.

The red dashed line - - - is explained just below at "backwards septic tanks".

This is insurance against pushing solids out of the tank when a toilet is flushed and the waste levels in the tank rise up briefly.

If we didn't have this insurance of the extra length on the outlet tee extension, the surge of waste into the tank might push some of the floating scum layer and sewage through the outlet where it would quickly clog the septic piping or drain field.

As we mention under diagnosing drainfield odors, the outlet tee also has the job of reducing the movement of gases back out of the tank into the drainfield.

If you agree with the inlet tee dimensions discussed above, that means your outlet tee is going to extend down from the bottom of the tank outlet 16" to 18".

Septic Tank Outlet Must be Below Septic Tank Inlet: Watch out for "backwards-tilted" Septic Tanks

Septic Tanks Can Actually Be Installed Backwards or May Settle & Tip! And tilted or incorrect septic tank elevations lead to sewer line clogs.

The red dashed red line - - - in our septic tank illustration above illustrates the 3-inch drop in elevation between the height in the septic tank of the inlet pipe opening and the height in the vertical tank wall of the septic tank outlet pipe opening. The red dashed line also shows the top of the liquid level in a properly functioning septic tank.

Watch out: In addition to recommendations for a longer outlet septic tank tee than inlet tee, at least equally important, the actual septic tank outlet pipe opening in the vertical tank wall will usually be about 3-inches lower than the inlet opening. The Alaska DEC septic tank installation manual explains this septic tank design details as

A built-in vertical drop of approximately three inches between the inlet and outlet pipe is common.

During installation [of a septic tank] if the inlet and outlet ends of the septic tank are reversed, water will back up into the building sewer [piping], stranding solids that could block the line. [3]

We have received a few reader reports of exactly this backwards septic tank installation problem that shows up as recurrent sewage line clogs between the house and the septic tank. In some cases these clogs were eventually traced to the septic tank having been installed "backwards" with its inlet end opening lower than its outlet end opening.

[Note that on occasion we see septic tanks that are symmetrical - with inlet and outlet ends at the same elevation in the tank - a design that depends only on the inlet and outlet tee length differences discussed above.]

No the fix was not to dig out the whole septic tank and turn it around.

Once the tank has been installed, excavation and removal and rotating of a backwards-installed septic tank is probably cost prohibitive.

But depending on the tank construction materials, it may be possible to adjust the inlet and outlet openings, sealing and repairing the tank end(s) as needed.

Watch out: if the septic tank was installed backwards, the elevation of the waste line entering or leaving the septic tank is also going to need to be changed - this is not a trivial job, especially depending on site terrain. It may be easier to effect the repair at one of the tank than the other - raising the inlet end, or adjusting the inlet and outlet baffles or tees.

Question: My apartment (6flats) septic tank inlet pipe is lower than the outlet pipe

My apartment (6flats) septic tank inlet pipe is lower than the outlet pipe .... previously the outlet pipe was lower than the inlet pipe,but now due to heightening of road and drainage the outlet pipe is higher than the inlet pipe and the waste water is not coming out of outlet pipe. ..please help me..tell me a solution for this problem.

The previous outlet pipe is closed due to new road and new drainage, I kept the new outlet pipe at least possible level to drainage but even then it is higher than the inlet pipe - Anonymous by private email 2020/06/16

Moderator reply: possible fixes for improperly-sloped septic tank, wrong inlet/outlet heights

That's difficult to fix, Anon.

It may be possible to modify the outlet end of the tank to install a tank tee with a lower exit point, though it's an enormous lot of trouble and expense. If the tank used baffles rather than a septic tank tee, the new outlet should probably use a tank tee that can extend a bit deeper into the tank to avoid the sludge layer.

Keep in mind that all of this reduces the settling time available to the tank so it increases the frequency with which the tank should be pumped.

Normally the bottom of the outlet pipe is a few inches lower than the bottom of the inlet pipe at a septic tank. 

The underlying problem is that when the septic tank outlet is above the tank inlet there is likely to be a problem of clogging at the tank inlet that risks a sewage backup in the building. 
An onsite expert would of course see more important information that I cannot, and so might give different advice. 

Minimum Steps to Avoid a Sewage Backup

But from what you've told me, the most-reasonable steps to take when the septic tank outlet is above the inlet opening are:

1. be sure that the inlet and outlet tank baffles or tees are at least adequate in height and depth so that the floating scum layer does not enter and block either the inlet or the outlet

2. monitor the tank inlet end - checking at least annually for a build-up that could block the inlet (and cause sewage backup in the building)

3. Have the septic tank pumped frequently-enough that the thickness of the floating scum layer does not get so thick that it enters the inlet baffle or tee area - discover this by checking the layer thickness when the septic tank is pumped. 

Details of a Proper Repair for Tipped Septic Tank

The inlet and outlet pipes need to slope 1/8" to 1/4' per foot of horizontal distance - otherwise they will clog.

I do not know a correct repair for the situation you describe other than having a septic or excavation contractor re-position the septic tank. To do that you would need to

1. have the tank pumped out

2. excavate around the tank

3. disconnect it from the inlet and outlet piping

4. lift the septic tank

5. add fill to properly level or slope the bottom of the excavated opening

6. replace the tank

7. reconnect its piping

8. restore the tank cover

All of that is a lot of trouble and expense. 

In a severely-tipped or improper inlet to outlet height septic tank problem a contractor might install an additional pumping chamber but all of this depends on getting effluent to the drainfield without clogging at that end as well.

My original thought was that one could excavate at the tank outlet end, disconnect the existing piping there, cut the tank wall to lower the outlet point, restore the pipe and seal the opening at that end.

But to do that while maintaining the needed 1/8" to 1/4" slope per foot of run in that effluent outlet line may be impossible without extensive additional excavation. 

 

Add a Filter at Septic Tank Outlet to Protect the Leach Field

Now if you want to add protection for your drainfield, you might add a filter at the outlet tee.

A number of companies sell these devices which will add life to your drainfield by reducing the level of suspended solids flowing out of the tank.

If you buy a septic tank outlet filter you'll see that the filter product will typically be of about the dimensions of the outlet tee we cited above, or perhaps an inch or two deeper.

See the links below for more information about septic filters and septic media filter systems.

See FILTERS SEPTIC & GREYWATER for details.

Question: where to connect sewer lines to the septic tank

2017/11/29 jake said:

can you pipe from house to top of tank

This question and reply were posted originally

at SEPTIC DRAWINGS

Illustration: connecting a PVC sewer line to the inlet end of a concrete septic tank using an asphalt based mastic adhesive/sealant. Adapted from the New Mexico Department of Environment system installation guide cited below.

Note: the incoming waste line needs to slope towards the septic tank no less than 1/8" to 1/4" per foot - in the photo we can't see that this line is sloped towards the tank - but it might-be.

Reply: waste lines connect to pre-fabricated septic tank inlet and outlet openings at the tank end baffles

Jake,

Septic tanks, whether made of concrete, fiberglass, or plastic, are designed with a single inlet and outlet opening at the inlet and outlet ends of the tank. (Take care to get the tank properly positioned as the inlet and outlet openings are not at the same height).

It is not only much easier to use the factory-provided septic tank openings to connect incoming waste and outgoing effluent lines than to try to cut and seal a do-it-yourself opening in the septic tank top, it is also more-likely to keep the septic tank working properly as I will explain here.

In reviewing our literature, standards, codes for septic tank installation I have not found any source that describes a through-top connection of the sewer line into the tank.

Watch out: do not bypass septic tank baffles when connecting piping to the septic tank.

Normal septic tank design that relies on baffles to control the flow of solids and wastewater into the tank, to control agitation inside the tank's treatment area, and to prevent the floating scum layer from blocking the tank inlet or outlet.

The entering sewage must flow into the septic tank where there is a baffle system. For multi-compartment septic tanks, the incoming sewage also must flow into the proper (initial) compartment.

Watch out: skipping the factory-designed pipe connections in order to cut a new opening into the top or sides of a septic tank risk damaging the tank, possibly causing the need for expensive repairs or even creating an unsafe septic tank at risk of sidewall collapse.

Watch out: undue agitation of sewage in a conventional septic tank resulting from a home-made top entry would direct waste towards the tank bottom where it can cause agitation of the tank's scum and sludge layers, leading to an expensive early failure of the drainfield system by pushing floating solids out into the absorption bed.

If you are piping from any height, dropping waste vertically into the septic tank from some other tank top opening risks undue agitation of the sewage, preventing proper septic tank operation. We want the sludge to settle, the scum to rise and we do not want to push solids into the drainfield.

Above: adapted from the New Mexico Environment Department Septic Tank Installation Guide cited below, we show a white PVC waste line being sealed to the septic tank entry port.

Take a look at this

• SEPTIC TANK & DRAINFIELD INSTALLATION GUIDE [PDF] A Homeowners Guide: Installing a Septic Tank and Drainfield NMED Liquid Waste Program Public Outreach and Training (2006) produced by the U.S. New Mexico Environment Department, originally developed by Adrian Hanson, Ph.D., PE: NMSU/Tejeda Center Craig Runyan: NMSU/Agricultural Extension Specialist Bruce Lesikar: Texas A&M/Agricultural Extension Specialist, retrieved 2017/11/29, original source: https://www.env.nm.gov/fod/LiquidWaste/Homeowner%20Notebook%20final%202006.pdf

The typical connections to the septic tank inlet and outlet ends using a neoprene collar to seal the waste lines to the tank. Where a neoprene collar is not used, the installer typically uses a fiber-reinforced asphalt mastic cement.

Diagnosing septic odors in the building, or in the septic tank or drainfield areas

Odors around the drainfield might be due to loss of the gas-baffle in the septic tank. Of course such odors may also be due to a failing drainfield, so further diagnosis is in order.

Checking the presence and condition of the septic tank outlet baffle (gas baffle) is done at the septic tank and should be quick and easy. If the outlet baffle is lost it should be replaced, but you should also assume that the drainfield has a somewhat reduced future life.

Failing drainfields may have been caused in part by a previous loss of the septic tank outlet baffle. Because lost septic tank baffles are both a possible cause and a diagnostic aid in the occurrence of septic system smells or odors, see the detailed articles on tracking down and curing septic or sewer gas odors inside or outside buildings listed at

SEPTIC & CESSPOOL SAFETY

SEWER GAS ODORS

SEWER GAS ODORS in COLD / WET WEATHER

TOXIC GAS TEST PROCEDURES

Diagnosing septic piping backups between building and septic tank

Backups at the waste line leaving the building, or apparent clogs in the pipe between the building and the septic tank could be caused by a lost septic tank inlet baffle which has led to clogging of the tank in that area, resulting in a slowed or even totally blocked flow into the tank.

If the plumber simply clears the line between house and tank, without repairing or replacing a lost septic tank inlet baffle, the repair will not be long-lasting.

See CLOGGED DRAIN DIAGNOSIS & REPAIR for help in diagnosing slow or clogged drains or septic backups;

also see

SEPTIC BACKUP PREVENTION.

Diagnosing septic piping leaks into the septic tank, flooding the tank and drainfields

See SEPTIC TANK BAFFLES for an explanation of how to observe clues at the septic tank baffles or tees to look for signs of tank flooding when opening the septic tank for cleaning, pumping, or inspection.

See SEPTIC TANK LEAKS for an explanation of how and why septic tank leaks cause septic system failures.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-06-07 by mak.church (mod) - sewage pillows at the septic tank tee or baffle

As nobody has found an obvious cause for the blockage you reported originally we're back to our earlier guesses; it's possible that when the tank was pumped the pumper didn't clear the baffle area.

When we worked with a septic pumper he called the square of floating scum in a conventional septic tank baffle "the pillow" and said that as he pumped the tank he would watch for the "pillow" to drop down into the floating scum that he was removing - pumping in that case from a septic tank access that gave view of the septic tank inlet end baffle, the septic tank center, or both.

If the "pillow" doesn't drop he gives it a poke with the same tool he uses to break up and pump out bottom sludge - looks like a giant hoe with a couple of holes in it.

A similar "pillow" of floating scum might accumulate in the lower end of a septic tank inlet tee where a pipe tee is used in lieu of the traditional baffle.

Another septic tank pumper may not have taken that extra care.

On 2021-06-07 by Kenneth - septic system jetted, not needed, working fine

I have given it a few weeks and inspected again and all looks good, and is clear, at least to this point. The water level sets right at the bottom of the inlet pipe, and after draining a large amount of water in, it only rises for a few minutes before being right back at that level.

Again, when I had my drainfield lines jetted, they didn't find any buildup, or any blockages of any kind and actually asked me why I was having it done. While I agree, it did go way too long in being pumped, I don't feel that it caused any adverse issues at this point. I've had everything cleaned, and inspected, and all seems good other than every 6-months to a year, the inlet now clogs when it hasn't for the previous 15 years.

Something just seems like it changed, and I don't think it's on the outlet side.

On 2021-05-14 - by (mod) -

@Kenneth,

That tank was, sorry to say, pumped very much too late.

When the solids are up to the tank outlet then the tank has been operating with NO net free area for probably years.

The "net free area" is the free liquid effluent space between the under-side of the floating scum layer and the upper surface of the settled sludge layer at tank bottom. We need enough net free area in a septic tank that we have at least 24 hours settling time on all incoming wastewater;

Without sufficient free area we have too little settling time.

With too little settling time, each time sewage enters the septic tank it pushes floating solids out into the drainfield.

The result is reduced drainfield life - the small floating solids clog the field trenches or soil.

The result leaves us pessimistic about the remaining life of any septic drainfield that has been operated with too little septic tank settling time.

I suggested checking the sewage level in the tank - if it's above the outlet by even a small amount that suggests either a blockage in the effluent outlet piping or a failed drainfield. That condition, in turn, can show up as blockage at the septic tank inlet.

The risk is a sewage backup into the house

ALL of this is theoretical as we can't see and don't know much about your specific septic tank, D-box, and Drainfield.

Most important is to stay safe; don't fall in the tank and don't get asphyxiated by leaning over it and into a cloud of methane. Best not to work alone.

On 2021-05-14 by Kenneth

I should have been more clear,,,, he did poke a rod of some sort down in the tank and stated the solids at the bottom of the tank were up right up to the bottom of the inlet so it definitely was time to pump the tank. (although, thinking back, it may have just been an inlet clog that caused the original backup). Being 15 years and no pumping, it's very possible it was full of solids, but no way to know for sure at this point.

As for jetting lines, when he was out the second time they dug up the outlet and stated it looked "ok", but since it clogged quickly they recommended a jetting. I'm thinking at this point they just used that as an opportunity to send some business to one of their buddies. Since I didn't know a lot about septic systems, I semi-trusted the guy, but had my concerns and no way to verify. Lesson learned for me, and have learned a lot since then in my search for solutions.

Based on these facts, I have my doubts there are any issues at the outlet, but I will confirm. As of right now I have the inlet side dug up, but the cover still in place since I just cleaned it out. I figure I'll give it a week or two and then just inspect and see what it looks like. The water level was down below the inlet just slightly and when I unclogged it then rose a couple of inches and went back down shortly after. I sure wish there was a simpler way to monitor, but i'll see what happens.

On 2021-05-13 - by (mod) -

@Kenneth,

Let's be clear and maybe sort out a point of nonsense:

Guy told you the septic tank was full?

Really?

Hey: a septic tank in use is ALWAYS FULL except for when it's first plopped into the ground and perhaps 1-3 days immediately after pumping.

In normal use the tank is full of sewage: floating scum, sewage, and settled sludge on the tank bottom.

A gallon of wastewater IN to the tank from the building it serves pushes exactly the same volume - a gallon - of effluent out the septic tank exit and into the drainfield or absorption system.

So telling you the tank is full is rather nonsensical unless - I am MAKING THIS UP as an example - perhaps the contractor was not an English major, doesn't use language precisely (except for what he'd have to call me), and maybe he meant that there was too much solid waste in the tank - meaning it was overdue for pumping . "Full?"

And FYI, jetting the drainfield lines doesn't hurt (probably) but will never fix a failed drainfield. The trenches around the effluent distribution pipes or "lines" become clogged with a thickened biomat; passage of effluent out of the pipes, through the gravel (that should be there) and into the surrounding soil slows, and finally stops.

Jetting inside the pipes or even poking around in the soil to try to "restore" the drainfield is a popular business, another of those magic bullets that crop up to try to kill off expensive problems that, unfortunately, don't work, miss the target, and offer little or no lasting improvement.

At the next "inlet tee" clog, take a look at the outlet tee and into the septic tank - have this done by someone who's trained as this is a dangerous process: leaning over an open septic tank can asphyxiate someone, and falling into a tank is usually quickly fatal.

Inspecting the sewage level at the tank outlet will tell you if the outlet's clogged and/or if the drainfield is not accepting effluent.

On 2021-05-13 by Kenneth

Agreed. I do know the guy that pumped it has been doing them for 20+ years and seemed to know his stuff. However, I don't know how 'shady' he could have been as well. He did tell me on the first pumpout that it was full, which is likely accurate. I did peek into the tank after pumping and all "appeared" good, to my untrained eye.

When it clogged 6 months later, i called him again thinking something had went wrong. He pumped it, said it wasn't full but it was clogged at the inlet. He dug up the outlet, said it may have an issue there are recommended jetting the lines. I had that done (expensive) but they didn't find anything wrong and said I was really only utilizing the first 2 of my 4 lateral lines. No roots, no clogs, and all was good.

Still no definitive reason for that clog. So, we buttoned it back up and 6 months later it did it again. This time I dug up the inlet, saw the clog, and cleared it. After that, it's just been a routine every 6 months to a year I have to dig it up and clear it. I'm just puzzled as everything seems good. Maybe it just needs more water to flush things through the inlet T, but that sure seems odd to have to do.

On 2021-05-13 - by (mod) -

@Kenneth,

That's the interesting question which we have both posed. Other than the reduction in wastewater volume, which should certainly never explain clogging at the septic tank inlet tee, we haven't got a proposed explanation just some speculation that I offered (changes to the tee that went un-noticed, change in septic tank floating scum layer thickness (I don't assume we know exactly what was "pumped" nor how-thoroughly), or something else that an experienced eye would spot on-site and that nobody can see by texting (e.g. abnormal levels in the tank).

You might want to have the sewer line between house and tank inspected by sewer camera and also to check the tank outlet end as that can affect outflow and thus inlet conditions.

On 2021-05-12 by Kenneth

Why would it change though? After 15 years of working perfectly, and then after pumping I start having problems every 6 months or so with no other changes?

On 2021-05-12 - by (mod) -

@Kenneth,

It's possible that the Tee extension down was just too long.

On 2021-05-12 by Kenneth

I watched the pumpout, and the tank was completely empty. The inlet T "appears" to be in good shape from what I can see, but I have not had it pumped and then inspected so it's really hard to tell. I did confirm there is a length of pipe on the bottom of the T.

I did not measure it, but best I could tell it is about 12"-18" inches or so. Effectively nothing has changed except we no longer have 4 kids at home that we had over the years, so possibly reduced water usage? Maybe more water was flushing everything down and now with reduced people in the house, there is less water flowing?

It has been about 3 years since the first pumping, and about 6 months after that a second pumping and line jetting since it clogged again.

Since then, I just dig up the inlet access opening and clear the clog myself, but I have to do this about every 6 months. Seems odd that I went 15 years with absolutely zero issues, and now I have to dig it up every 6 months or so.

On 2021-05-12 by (mod) - possible caused for sewage backup and/or blockage at septic tank inlet

@Kenneth,

I can't see your system so can only offer speculation, but

if the septic tank inlet Tee never clogged prior to a recent pump-out and line jetting it's possible that the tee was

-damaged

- moved

- removed

- changed

or that the pumping operation itself failed to remove the "pillow" of floating scum and solids that can remain in and around some septic tank inlet baffles.

Solid flowing in any sewer line can impact, stick, and cause blockage at elbows and tees, particularly if the Tee is an abrupt change in direction rather than a wide sweep sanitary tee.

Let's look further at what has changed.

On 2021-05-11 by Kenneth

Our septic system worked great for 15 years with 0 clogs of any kind. We eventually had it pumped out and ever since then we have had the inlet T clog every 6 months to 1 year. I have dug up the access at least 6 or 7 times in the last few years. We even had the lateral lines jetted and all checks out good, but it keeps clogging. The inlet T appears to be in good shape, what could be the issue?

On 2021-05-07 - by (mod) -

@Brandon,

A 4-inch to 6-inch plastic T is probably a $20 part.

Everything about the cost of the repair of a septic tank baffle is going to depend on the condition of the tank, the tank cover, and the amount of excavating needed to gain access.

There's no single credible answer one can give to that because it ranges from 10 minutes to open an existing septic tank lid on a safe concrete cover to hours of work to find, dig up, access and repair a buried septic tank.

Therefore the cost of replacing a septic tank baffle with a t could range from a few hundred dollars to thousands.

On 2021-05-04 by Brandon

About how much would a repair to the inlet baffle cost me on average?

On 2021-04-21 by Anonymous

@david tubbs,

Measure the internal dimeter ID of the exit effluent line at your septic tank

You should be able to buy a PVC Tee with a male insert end that fits right into that opening.

On 2021-04-21 by david tubbs

i need to replace the exit T diameters available

On 2021-01-21 - by (mod) -

Keith

What your plumber says makes sense from a cost and practicality point of view.

But I don't quite understand your question #1. The sewer line has to get to the septic tank and should enter it at the septic tank inlet NOT at at a septic tank access riser - otherwise we have sewage entering the tank with no tank baffle. Now I emphasize that your onsite expert sees and knows more about the situation than I do. So he or she may be dead right.

If the "solution" (question 2) is a new tank tee installed at the riser (this isn't a design I've encountered) that might work as described.

Consider that the purpose of a tank tee or baffle, in the first place, is to prevent raw sewage from blocking or backing-up into the incoming sewer line; In your new design without that vertical extension on the tank tee (that 5 ft piece you cite) the sewage simply falls down splashing into and agitating the septic tank contents. I'm not clear on what problems, if any, that might create.

I'd like to see a sketch of the design.

Has your installer tried this solution before?

Why is your tank so deep? Does that depth mean that the drainfield is also quite deep in the soil? If so I'd not be optimistic about the drainfield's ability to fully treat sewage effluent pathogens as it may be oxygen-starved.

On 2021-01-21 by Keith

My house has a 3" "Orangeburg" pipe from the building to the septic tank which is collapsing and must be replaced. A large tree makes digging up and replacing the pipe impossible. My plumber has recommended that we abandon the existing pipe and tee, and route the new pipe from the house to the septic riser (rather than directly into the tank).

This would result in the pipe being several feet higher at the entry than the original, but it would still have the required slope from the house. My questions are:

1. Is it permitted to terminate a drain line into a plastic riser instead of the side of the septic tank?

2. If the pipe is terminated at the riser, and a new tee is installed at that location, should the bottom of the tee extend all the way down through the floating scum layer like the existing tee? This would make the bottom of the tee approx 5' long.

On 2020-09-02 - by (mod) -

Nathan you may be able to may be use a rubber Hubble or similar connector to attach new pipe to the stub of the existing one. Try touching a photo so that I have more information and I can think about the problem more.

I've also used concrete, taking care to keep it out of the piping interior.

On 2020-09-01 by Nathan Fairchild

The input clay pipe that connects the house to the tank is damaged. We dug into the area and it appears the pipe was converted into the wall of the concrete tank, installed in 1960.

As an extra challenge, the wall is 12” thick. Service wait time is over two weeks and I’m afraid to remove the old pipe and discovery I can’t get it out of the wall, leaving me up sh*t creek. Thoughts?

On 2020-06-27 by Anonymous

Quinn

I'm not sure if you're asking about the height of the opening for the inlet and Outlet pipes or the dimensions of the plastic septic tank tees themselves. There's no single right number for those instead we Define them by making sure that the D is deep enough to be in the liquid upload and high enough to not get over fluid at its top. The specifications are in the article above. Please take a look and let me know if that makes sense to you.

It is important to note that the outlet opening bottpm should be 1 2 3 in lower than the bottom of the inlet opening

On 2020-06-27 by Quinn

what is the height of the inlet tee and the outlet tee on a 500 gallon septic tank with no compartment?

On 2020-06-27 by Anonymous

what is the height of the inlet tee and the outlet tee on a 500 Gallon septic tank? no baffle

On 2020-06-17 17:40:41.381130 - by (mod) -

Syed also wrote by private email:

My apartment(6flats) septic tank inlet pipe is lower than the outlet pipe....previously the outlet pipe was lower than the inlet pipe,but now due to heightening of road and drainage the outlet pipe is higher than the inlet pipe and the waste water is not coming out of outlet pipe...please help me..tell me a solution for this problem.


Moderator reply:

That's difficult to fix, Syed.

It may be possible to modify the outlet end of the tank to install a tank tee with a lower exit point, though it's some trouble. If the tank used baffles rather than a septic tank tee, the new outlet should probably use a tank tee that can extend a bit deeper into the tank to avoid the sludge layer.

Keep in mind that all of this reduces the settling time available to the tank so it increases the frequency with which the tank should be pumped.

On 2020-06-17 by Syed Sohail

My apartment (6flats) septic tank inlet pipe is lower than the outlet pipe, due to the new road and drainage construction the previous outlet pipe which was lower than the inlets pipe is closed.how to fix it.

On 2020-04-28 - by (mod) -

GT

I have not found an authoritative answer to your question, but there are, of course opinions. I think what's "best" depends on more factors than are present in your question - perhaps other features of multi-compartment septic tank design.

Elaborating: a "tee" or baffle system keeps floating solids from passing out of an opening, allowing just effluent to pass.

That's why conventional septic tanks use a tee or baffle at both inlet and outlet ends of the tank - to keep from clogging piping at inlet or drainfield at outlet.

In a mult-compartment septic tank with only a lower open hole to allow effluent to enter the second compartment, there's no need for a tee since the floating scum layer is higher in the tank.

On 2020-04-28 by gt

Some tanks with 2 compartments use a tee system between compartments and others just have a lower open hole between compartments. Which is best and why?

On 2020-03-08 - by (mod) -

No, John, a 4-inch septic filter needs a 4-inch diameter septic tank outlet tee.

A 3-inch outlet from a septic tank to the drainfield is a bit small and modest;

but in any event you might be able to have your installer simply use 3" to 4" PVC adapter to allow replacing your 3-inch outlet tee with a 4-inch tee that can accomodate the septic filter.

An example of such an adapter is shown below.

On 2020-03-06 by John Growney

I have a conventional septic that is 5 years old and was interested in putting a 4" septic filter in the septic discharge to the drainfield.

The problem I have is the the discharge tee is 3 inch and I see no 3 inch filters on the market.

May be Im confused but can a 4 inch filter fit into a 3 inch tee?

...

Continue reading  at SEPTIC TANK BAFFLES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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