Septic Tank Sewage Level FAQs

Causes of Abnormally High Sewage Level in Septic Tank FAQs

Tip: see the diagnostic and repair advice at SEPTIC TANK BACK FLOODING 

High sewage levels in my septic tanks: will an enzyme drain cleaner fix my failed septic system?

When my two septic tanks were pumped out recently, I was told by the operator that the level in both tanks were high and I need to replace the drainage fields for an estimate of $10,000.

There have been no problems in the house or around the drainage fields such as backup, smells or ponding water.

I am questioning whether there really is a major problem at this time. Could I use an enzyme drain field cleaner and wait and see if any repairs are really needed? On 2022-06-29 by Lisa -

by InspectApedia-911 (mod) - some septic repair kits show little success; enzymes won't fix your septic tank.

@Lisa,

It would make sense to have the lines scoped with a sewer line camera to be sure that there is not an easier repair needed such as repairing of a blocked or broken waste line.

But in genera,l your septic contractor is right. Though the price sounds a little low to me.

Although Magic Bullet septic repair kits like the one you describe are very tempting, there is not any record of ever finding long term or even intermediate term success with that approach.

How did our septic tanks get full of water before they are hooked up to the house?

We have had a sand mount new septic system installed, plastic septic system and dosing tank with a pump. We have not hooked anything up to the house yet and they are both full of fresh water.
The certified installer says he does not know why.

We know these tanks are S/b be water tight. The installer does not see anything wrong with this. We refuse to hook up to the house until this is resolved because the pump will keep running and burn out. The installer is threatening small claims court because we are holding back 5,000 and have thus paid him 15,000. He has not put any fresh water into the tanks for testing nor has done any testing.

Might you have any ideas why this is happening. We suspect the backhoe person might have damaged the tank or one of the intake or outage valves is not sealed. On 2016-12-22 by Bonnie

by (mod) - if new septic tanks are already full of water even though not connected to building

Bonnie:

If the septic system is not hooked up to the home and two tanks are full of water I can think of these explanations:

1. the tanks are lightweight fiberglass, were not anchored in the ground, so the installer, to prevent the tanks from floating up out of the ground in event of wet weather, filled them (this would be unusual, anchoring is preferred, and where would they have obtained the water?)

2. There is a leak somewhere and groundwater has entered the system through a leak such as you suspect: a damaged tank or a damaged pipe leading to a tank.

I think I'd inspect the tanks and piping, pumping the water out if needed, and using an inspection camera system in piping

Causes of Abnormally Low Sewage Level in Septic Tank FAQs

Septic tank is Not Full; is this a sign of trouble ?

I have a depression in the land around the septic tank.Area is dry. Was going to have tank pumped, but only half full. It's a 1500 gallon tank. On 2017-09-22 by Jane A Collins

by (mod) -

Jane,

It appears to me that you are describing a septic tank that is damaged and leaking. Such a tank needs to be repaired or replaced.

Does a drop in sewage level in the septic tank mean there are leaks?

I have a 500 gallon steel septic. I had this inspected for a sale of the cabin and when inspected the water level went down .25" over a 24 hour period. he said this is fine.

Is this true?

I got a second opinion and they just said water level was low and it [the septic tank] needed to be replaced.

Even though I told them our place has been vacant for 2-3 years.

Just trying to figure out if I need to replace this tank for my buyers. thanks (Feb 18, 2015) AA

Reply: leaks in a steel septic tank will drop the effluen level below the tank outlet pipe: that means it's time for a new (larger) septic tank.

1/4" is not much but can indicate trouble - a failing drainfield or. Rusted through, leaking steel tank.

A new system is in your future at any rate.

Watch out: No current sanitary code will find a 500g septic tank big enough. A true inspection should have commented as well on the tank baffles and starting tank level. High suggests failing drainfield as well.

In an inactive septic system, can low effluent in the septic tank be due to evaporation?

I have a tank that is suspected of leaking because the effluent level was lower than expected.

Everything I read indicates that the levels are low for an active tank.

If the system had been unused for over a year, could the levels be lower simply from evaporation? (May 16, 2015) Charles

Reply: Not likely unless the level drop is just an inch or so over a year or more.

Charles I can't guess from your brief e-text, but generally the evaporation rate from a closed septic tank is trivial.

When the tank is pumped and cleaned have its interior inspected (by a professional - NEVER enter a septic tank or even lean over it or that can be quickly fatal) for damage. Also check for leaks around the inlet and outlet piping.

Bottom line: Septic effluent that has fallen less than an inch below a septic tank that has NOT been in use for several months or longer, may be due to evaporation or transpiration, but for shorter periods of dis-use or for effluent levels that have fallen further the tank is probably leaking.

We have a "suspected" tank leak based upon a low sewage level - due to limited usage?

I've a question about a "suspected" tank leak based upon a visualized low sewage level in a rarely used concrete tank.

My sister ( widowed & 80) is selling her rural home with a "walk-out" basement. House is 25 years old. It has two septic tanks & fields. The one serving the main floor is 25 yrs old has previously been pumped and will be pumped again before selling.

This tank receives water from2 full bathrooms, a washing machine, and kitchen with dispose-all. The house has had two residents through most of this time and only one resident for the past 6 months. The house has also been vacant for 3 months each winter for seven years. (snow birds) An inspection revealed no problems with THAT tank. BUT....

The walkout basement has a separate 500 gallon tank and field. The inspector wrote in his report that he "suspects a leak" based upon a low sewage level in the tank. But he also noted that the tank contents did not need to be pumped.

The tank was installed about 15 years ago. THAT tank serves a single toilet. That is all. (The shower & sink drain into a separate gray water system that was supposed to be run into the tank at installation.

She has just learned that that connection was NOT made at the time of the septic tanks installation. She is hiring a plumber to do that. The buyers are asking for the tank to be replaced based upon the suspicion of a leak.

Is it reasonable to presume that the low sewage level in that tank is due to limited usage? She suspects that that toilet has not been used more than 4 or 5 times in the past year. At the most! (And that the toilet in-fact, has probably not been used more than 4 or 5 times a year for the past 5 years.) Any thoughts or guidance will be appreciated.) On 2022-02-17 by Gary E. Bachman -

by Inspectapedia Com Moderator - could low sewage level in a tank be due to limited usage?

@Gary E. Bachman,

Since a septic tank is water tight and covered, the liquid loss by evaporation (some septic tanks do have vents to the above ground airspace) is normally very slight. Regular but low-usage volume would not explain an abnormally low septic tank level in that case.

So unless a septic tank was pumped out and then its usage was so slight that it was not re-filled, I suspect that there may be a septic tank leak.

In my opinion it would be worth having both septic tanks pumped and the sides washed down and that wash water pump as well.

A good septic pumping company can do that for you. When the septic tank has been pumped then it can be inspected for evidence of leaks or damage. It would be a lot less expensive to put it into the question by actual objective data than to speculate and throw money at it.

Septic Tank Pumper says low level in septic tank means it leaks; isn't there a tank bottom drain?

Pumper claimed there is probably a leak in my concrete septic tank due to a low level of scum/effluent.

Not sure how much below it was from the outlet pipe invert. Home was used by six people for one week about 2 months prior to pumping. Other than that it is used just once a year for a week or two.

House/septic tank is 40 years old with good maintenance.

Neighbor states some tanks have a drain hole in the bottom that may be plugged or unplugged, if unplugged, letting water drain out slowly. On 2016-08-05 by jimolsen

by (mod) - no; septic tank bottoms don't use a drain; your tank is probably leaking; open, clean, and inspect

Jim the pumper's surmise is reasonable; why not check the tank levels when it's in use, then check it again when it's been out of use for a few months; normally the tank level will fall very little as there is little evaporation out of a closed septic tank.

I am not aware of any septic tank with a bottom drain feature. To me that makes no sense at all and sounds more like a suburban legend. Where would that drain drain-to? How would one access such a drain? Why would it be used? How would opening a tank bottom drain remove inches or more of settled sludge nor floating scum from a septic tank - the objectives of cleaning a septic tank?

When the tank has been completely pumped and cleaned out your pumper can inspect the tank for visual evidence of damage, cracks, holes. Certainly steel septic tanks rust out and leak; concrete tank leaks or fiberglass/plastic tanks are more rare.

When we opened the septic tank to pump it we saw it was just half full

I purchased a 2004 Florida home in 2008. After a few months I hired a 'Pump Out'.

We (the operator and I) found the tank to be 1/2 fluid filled to top and a large brick of effluent floating atop. Assuredly, the house had been empty for some time and the tank had dried out and solidified.

The tank was pumped, the effluent filter cleaned, the brick remained. Now, 11 years (900 gal/ one occupant) later, I am planning another pump out. Will that brick have dissolved and been digested?

I feel I should have insisted that it had been removed the first time I saw it. I was a first time homeowner and I didn't know. What if I (we) find it again, how can should it be dealt with? On 2019-10-31 by KurtS Curtis

Answer by (mod) -

Thanks for the question Kurt.

A septic tank, even when not in use, will normally be "full" of sludge (on the bottom), sewage (in the middle) and scum (a floating crud layer on top); the sewage level - the liquid level - will normally come up to the very bottom of the septic tank outlet pipe.

So if you open a septic tank and the top of the scum layer is at mid-tank, the most likely the tank is damaged and leaking - seeping effluent into surrounding soil. Unless the tank sat open to the atmosphere for years, it ought to have been full.

You never pumped the tank since 2008. Take a look at SEPTIC TANK PUMPING SCHEDULE https://inspectapedia.com/septic/Septic_Tank_Pumping_Schedule.php and you'll see you are EXACTLY on schedule to pump the tank now.

The "brick" will NOT have dissolved nor digested; it's a coagulated layer of oils and floating solids atop the sewage in the septic tank.

An effective septic tank pumpout operation will require that the pumper break up the floating scum layer and pump it out during the tank cleaning process. Sometimes the pumper will even need to add water (from a garden hose) to provide enough liquid to break up and pump out the solids at the tank top and bottom.

Details of that procedure area at SEPTIC TANK PUMPING PROCEDURE

Watch out: some septic pumpers don't do the real job of cleaning the septic tank.

For example, just poking a pumper hose down through a narrow 8" diameter access pipe into the liquid center of the tank and pumping out that material will not and cannot break up and remove the scum layer nor all of the sludge layer.

Better to open the tank's access port - removing a cover (not the whole septic tank top) to give the pumper access space to reach into the tank with a tool (similar to a giant long-handled hoe) to break up the solids during the pumping operation.

Worse, some septic pumpers run a scam of pumping the tank the returning some of the now macerated pumped sewage back into the tank. Do not permit that - it increases the risk of an early drainfield failure by sending macerated floating solids out into the drain field.

See details at RETURN SEPTIC "WATER" BACK TO THE SEPTIC TANK? - Not Recommended

Could our vacant house septic tank sewage top level fall 8 inches in 5 months from just evapoarion

We're selling our house and it's been vacant for about 5 months.

Septic inspection shows the liquid level is 18 inches below the invert of the outlet line, indicating that the tank is leaking at the midseam.

Since the house has been empty for 5 months, could this be due to evaporation/transpiration instead of a leak? Is there a way to tell which it is? Thanks for any help.

by (mod) - septic tank loses little liquid by evaporation

It's not likely that a tank would lose 18" of liquid by evaporation even over 5 months.

You could have the tank pumped and its interior inspected by a pro.

Watch out: DO NOT try leaning over nor looking into the tank yourself - that can be fatal.

We see low septage levels due to a cracked septic tank - do we still need to pump?

The liquid level low due to suspected crack in septic tank, should we still have the sludge pumped?

by (mod) - pump the tank and find the leak so that it can be fixed

Hilda,

I would have the septic tank pumped and thoroughly cleaned so that my septic contractors could inspect the tank to determine where damage is present as well as whether or not repair is cost - reasonable.

Watch out: never lean over nor attempt to enter a septic tank as doing so good result in death.

Normal Septic Tank Sewage Levels FAQs

Will the septic water always be within inches of the top of my septic tank?

I have a 1200 gallon tank that was installed new 6 years ago. It is taking care of a rented duplex unit (2 famly) I recently had it pumped out. When I looked into the tank I saw water and other things floating within aprox 4 inches from the top.

When I commented to the tank truck guy that it looks as though the tank was full and needed pumping out he said yes. When I mentioned to someone else that the tank was full I was told that the tank is always operating with the water up to within inches of the top of the tank.

So I ask you ifI remove the cover from the tank at anytime will the water level always be that high? Thank you in advance Bill On 2011-11-18 by william rebman

Answer by (mod) - normal levels of sewage that should be found in septic tanks

William:

We describe the normal levels of sewage that should be found in septic tanks in the article titled

• SEWAGE LEVELS in SEPTIC TANKS

Remember that a normally operating septic tank is always full, right up to the level of the exit pipe that drains off effluent to the drainfield or soakaway bed.

Abnormally high sewage levels in the septic tank are any levels above the outlet pipe - indicating a blockage, clog, or flooded drainfield.

Abnormally low sewage levels are any level below the outlet pipe, usually indicating that the tank has a leak.

Exceptions to low levels include, of course, the period right after the septic tank has been pumped.

Depending on septic tank size and the level of its usage, number of building occupants, amount of wastewater sent daily into the septic tank, it can take a few days for it to refill after pumping.

My septic tank is nearly full: should I get it "emergency pumped" ?

I have a tank that is 8'4" long by 5' wide. It hasn't been pumped in 4 years. The liquid level under the tank access is 8" to the top of the tank. The septic company is telling me not to worry that I can wait until the 14th which is 9 days away. Two people living here, moderate to light water use.

Should I pay up for emergency pump out or wait. On 2015-11-05 by Tank Level 8# headspace

by (mod) - how long to wait to pump a "full" septic tank

Tank

NOt to worry: as long as you're not having a sewage backup issue, you can certainly wait nine days.

It is perfectly normal for the septic tank to be always "full" to a few inches from the top of the tank. That's how septic tanks work.

The tank is always full (except for a few days right after pumping); when you send wastewater into the septic tank, the entering waste pushes a like volume of effluent out of the septic tank at its outlet pipe where that effluent passes on to a soil absorption system, drainfield, leachfield, soakbed, or soakpit.

See SEPTIC TANK LEVELS of SEWAGE - to read details.

Is it normal to pump a septic tank at 9 or ten months with normal use?

Had a 1500 Gal. aerobic treatment unit installed. Used by a family of 2 adults and 4 children under 12yrs.

Was told I have a 1" scum layer and 12" sludge layer and pumping is recommended.

This unit has been in use for 9 months. No garbage disposal. I was told it would need to be pumped every 3 to 5 years depending on use. Is it normal to pump a tank at 9 or ten months with normal use? (Aug 27, 2012) Matt

Reply: no

No. Either the tank is improperly sized or something else is wrong. Or the pumping is not necessary.

The meaning of "1 inch of scum" and 12" of sludge depends on some important questions:

An inch of floating scum is very little and alone would not normally be a reason to pump the septic tank; but we need to consider the sludge layer at the tank bottom, too.

If the septic tank is too small then even a modest thickness of those layers leaves too little net free area for effluent treatment to occur - solids will flow into and ruin the drainfield

Watch out: If the previous septic pumpout job didn't really clean the septic tank - that is, if the pumper just removed effluent and left the scum and sludge (a very bad job) then sure, the next time someone looks those levels will be "high".

If the septic tank isn't too small the pumping contractor may have been perhaps a bit conservative?

Septic Tank Tipped out of Level FAQs

New septic tank is 4-inches higher on inlet side: what does this mean?

Two weeks ago we had a septic system installed. We have now discovered the cement tank was not placed level in the hole. It sets 4" higher on the inlet side. What if any are the future reprocussions of not having this properly leveled? Thank You On 2017-05-08 by gmelch79

Answer by (mod) - The septic tank inlet should be 2" or more above the outlet pipe

GM

It would be a serious problem if the outlet were above the inlet, but the reverse might not be a problem.

You should confirm that the tank is working acceptably by having it inspected at the inlet and outlet ends to double check that the septic tank baffles at the low end are not being flooded over the baffle top: if that's happening there would be a problem: solids clogging and ruining the drainfield. It's repairable by installing a tank tee to raise the baffle top above the sludge level.

If the outlet baffles are working then at most a tipped tank means that there is a small reduction in effective septic tank capacity - provided that the tank is otherwise set on solid soil and that it won't settle and tip further.

Watch out: If the septic tank settles and tips further then it will break its plumbing connections and further repairs will be needed.

So check its condition again at the end of your wet season - (that depends on where in the world you live).

Keep me posted.

Toilet Backup Traced to Septic Tank Pumpout Troubles?

Our toilets back up, the sewer lines are not blocked, what's wrong?

I had a toilet back up twice. camera revealed no blockage. Look inside septic and water is flowing constantly. Completely shutoff all water to the home yet septic has constant water running into it? (Nov 3, 2014) stacey

Reply: look for a flooded drainfield or groundwater leaks into the septic system anywhere

If water is flowing in the septic tank and all water in the building has been shut off, including toilets or tanks that could be draining by gravity into the building drain system, then the water is from an outside source, such as ground water leaking into the septic tank or a flooded drainfield back-flowing into the septic tank.

Toilet backups traced to septic tank flooding traced to leak at septic tank inlet pipe

I had a toilet back up twice. camera revealed no blockage. Look inside septic and water is flowing constantly. Completely shutoff all water to the home yet septic has constant water running into it?

I found it! The problem was a leak at the septic tank inlet pipe connection: ground water was leaking into our septic tank! 11/2/2014 stacey

Reply:

Nice going, Stacey. That was my guess. Now the questions are how to keep surface runoff or groundwater not only out of th septic tank but also out of th drainfield.

Slow flushing toilets, septic tank level is below the outlet pipe: Will septic tank levels diagnose the problem?

Our one toilet is flushing slowly and other upstairs was between slow and flushing. So I checked the septic tank which was replaced 5 months ago.

The sludge-liquid line is about 6 inches below the outlet pipe where the filter is.

There is also still water at the bottom of the pipe that the filter is in. Shouldn't this water drain out of the pipe into the new tank ?

I have a picture I can email you but do not have your email address ? Thank You Nov 24, 2014) Joe

Reply: Yes if the septic tank is blocked, flooded, or clogged

Joe to send photos use the email found at the CONTACT US link

Normally the tank liquid level will fill to about the bottom of the outlet pipe. Floating scum will be above that point.

If liquid waste is below the septic tank outlet and the septic tank has been in recent use, there is probably a leak in the tank itself. So you could still have a clogged failed drainfield that causes toilet backups when the plumbing system is in more active use.

Or there may be a partly blocked drain line between house and tank.