Septic system D box FAQs:

Frequently-asked questions and answers about septic system distribution boxes or D-boxes: what is a D-box, where is the D-Box, why do we need a D-box, and how do I fix or replace a D-box?

In this article series about septic system drop boxes we describe the best procedures for locating and inspecting, repairing or replacing the septic drainfield distribution box, or the "D-box" or "Splitter box".

Septic System Effluent Distribution Box Questions & Answers

These questions and answers about the distribution box or D-box used for septic system effluent line connections were posted originally at SEPTIC D-BOX INSTALL, LOCATE, REPAIR - home - be sure to review the advice given there.

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On 2020-06-06 by (mod) - smelly water standing in the back yard for a couple of years

Anneka

That sounds to me as if the septic drainfield has failed and needs replacement.

On 2020-06-06 by Anneka - septic tank fills up very quickly

My septic tank fills up very quickly. We've had smelly water standing in the back yard for a couple of years. We recently had the tank cleaned and a couple of days later the d-box was cleaned. About a week later, the d-box had water standing on it again with no rain.

The grass is pretty green where the drain lines are running so we can tell that it's feeding to the lines a little. What could be wrong.

On 2019-12-09 - by (mod) -

Roger

I don't see any problem with that idea at all, as long as you can line up the incoming and outgoing pipes without messing up their relative elevations

On 2019-12-04 by Roger

i have a broken concrete distribution box and replaceing it with a plactic box can I leave the bottom of the broken box in place and put the new one on it for stability being it’s already solid and level

On 2019-04-19 - by (mod) -

Pat

Because the d-box or distribution box is basically a junction box connecting a single septic effluent input line into one or more outlet drain field lines if the box is flooded or even if it simply has liquid above the bottom of the outlet pipes than the drain field is either blocked or has failed.

On 2019-04-18 by Pat

Recently had house inspection and the D Box was found to be full. Please give me some reasons why the D Box did not distribute the water. The system is 30 years old.

On 2019-03-06 - by (mod) -

Oz that would be an odd requirement; you're simply repairing a damaged pipe and D-box, not moving nor rebuilding a drainfield. Of course the final legal authority is always your local building department.

On 2019-03-06 by Oz Quinones

Is a perc test needed to replace outlet pipe and distributor box on septic system?

On 2018-12-04 by Anonymous

f anyone could please help me I would be so thankful.

Over the pass 2 years we have been having to have our Septic tank pumped out about twice a year.

The last time was 10 days ago.

We have never had water back up into the house but the toilets will get where they will not flush or the Bathtubs will start draining very slow then we know it needs to be pumped,

After having it pumped this time we dug up where the distribution box should have been.

To only find that it had disintegrated the only thing that was still there was a concrete bottom. There is a pipe that runs out the septic and across from it is another pipe that runs out to the drain field and to the left there is 2 other pipes that are side by side.

I bought a Polylok 4-Hole Distribution Box with a Solid Cover to replace the old box.Where the box goes is under water we were able to get the water out the area do you think it is holding water cause there is no distribution box to push it out to the drain field?

Was able to get 50 feet of water hose in the pipes running to the drain filed,any help would be really appreciated..

Thanks

On 2019-05-08 by (mod) - a clog that needs to be cleared.

Carol

From your description it's possible that there's a clog that needs to be cleared. That's not something we could discuss usefully by telephone you need an on-site plumber to perhaps use a sewer line camera to inspect your lines. If the leach field is in failure or you'll know because you'll see that it's flooded.

On 2019-05-06 by Carol

I having a problem with my leach field not draining properly. I installed a leach field 5 yes ago.

Someone said it might be the d box does that sound like it could be that,? I had a backup last year in my waste pipe my tenant poured grease down my kitchen sink and put baby wipes and female products down the toilet. I had the pipe snaked and everything was fine until now
My home is in milton NH.can u call me 941 221 1970 tks carol

On 2019-04-15 by (mod) - How can I diagnose if my issue is the D-box or seepage pits?

JP

Please see your question repeated and my detailed reply at

See details at

SEPTIC D-BOX SPLITTERS

On 2019-04-15 by JP

How can I diagnose if my issue is the D-box or seepage pits? Also can you tell if there is a diverter valve from these picture? I recall that my septic inspector (15 years ago) said something about selecting and alternating pits. I am not sure how to do this. Any recommendations?

On 2019-04-08 by (mod) - Do all tanks have a dbox

Typically yes but not necessarily always. For example of septic tank that empties into a seepage pit doesn't need a DI box because only one exit line is leaving the tank

On 2019-04-07 by Anonymous

Do all tanks have a dbox

On 2019-03-28 by (mod) - there is no reason that a septic contractor would automatically include a new D-box when replacing a septic tank

Mike

in my OPINION there is no reason that a septic contractor would automatically include a new D-box when replacing a septic tank, but it would make sense to have investigated the condition of the septic system to determine if the D-box is in good condition, since it's always less expensive to do the whole job at once than to have to return to a site.


Craig:

Technically you could splice in a new D-box elsewhere BUT you are likely to have to do an enormous amount of digging and there could be problems maintaining the require slope on the drain or effluent lines.

That's because currently it's likely that the various leachfield lines that are brought to the existing D-box run off in different directions. You'd have to find each of those, intercept it, rout a new line to a new D-box and connect that to the septic tank, all the while keeping the slope of 1/8 to 1/4" per foot on the drains for the system to work.

It might make sense to open the floor of the shed.

On 2019-03-28 by (mod) -

Mike in my OPINION there is no reason that a septic contractor would automatically include a new D-box when replacing a septic tank, but it would make sense to have investigated the condition of the septic system to determine if the D-box is in good condition, since it's always less expensive to do the whole job at once than to have to return to a site.

On 2019-03-27 1 by Mike

I got a quote for $12k to replace my septic tank. The contractor wants to charge more for the d box replacement because he couldn't anticipate it was bad. I had another quote from a company I should have used that included the d box for the same price $12k. Is it common to replace the d box at the same time as the tank (55 year old system).

On 2019-03-19 by Craig

My d-box is located under a large shed making access impossible. Is it possible to splice in and install a new d-box?

On 2019-03-12 0 by Rod

I'm making my own distribution box. What is the dementions of said box supposed to be?

On 2019-03-06 19:23:27.253047 by Oz

Is a perc test needed to replace septic outlet pipe and distributor box?

On 2018-09-23 by (mod) - I had to replace my d-box

that looks ok to me

On 2018-09-22 by Todd

I had to replace my d-box and rather than having the leech line enter the box at it's current level (about 9 inches below the inlet), it seemed like a good idea at the time to use 2 elbows to create a drop, making the line enter the d-box slightly higher (about 2 inches below the inlet). See pic. Now I'm questioning if this was a good idea.

On 2018-08-14 by (mod) - normal for some liquid in D-box

That would be normal if there is liquid in the bottom of the D-box - below the bottom of the outlet openings.

If you see water above the D-box outlet openings then those drainfield lines are clogged and failing or are being flooded by rainwater or both.

On 2018-08-13 by Wayne

Does d box always have some water in it when not using system?

On 2018-07-09 by (mod) - where to measure slope of a septic drainfield pipe

thanks for the interesting question. It doesn't matter where you measure as long as you make the measurement at the same point on both ends of your Piper trench.

That is you can measure the bottom of the pipe where the top of the pipe to slope needs to be the same.

On 2018-07-06 by Tom

When measuring the 1/4" slope from the tank to the d box do you measure from the top ,middle or bottom of outlet
Thanks

On 2018-03-07 by (mod) - The D-box needs to feed the up-slope end of the drainfield lines.

Marcus

The D-box needs to feed the up-slope end of the drainfield lines. If you feed into the middle of a properly-sloped leachfield line you will miss using the upper half of the system, will overload the system, and will shorten its life.

On 2018-03-06 by Markcus

Can u come out of the d box and tie into the middle of fill lines or does each line need to be tied to each end

On 2018-03-07 by (mod) - The D-box needs to feed the up-slope end of the drainfield lines.

David

When effluent in a D-box is above the bottom edge of the D-box outlet pipe(s) then the drainfield is indeed flooded and failing.

Saying that the "D-box is operational" sounds confusing.

For a D-box to "sink" placing liquid level over the drainfield outlet would not change evidence that there is standing effluent or water in the drainfield lines.

On 2018-03-06 by David

Hello, I had a inspection done on my septic system for a pending sale, and the system was satisfactory but with a concern.

The concern was the water in the d-box is above the invert when running, the septic tank and field were satisfactory. what does this mean?

it does not appear to be clogged and they stated the d-box is operational and not leaking

? is it possible the d-box sunk and even though the effluent in running out it just is not out as fast as it should?

On 2018-03-02 by (mod) - maximum distance the leach field can be from the d-box?

Amy,

Not by code, but in a practical sense since you need to have an eighth to a quarter inch of slope per foot on the drain lines or leach field lines

or lines from the d-box to other leach field components, you can see that if the distance is quite great your Fields may be too deep below the surface of the ground to be either effective or economical.

On 2018-03-01 9 by Amy

Is there a maximum distance the leach field can be from the d-box?

On 2018-02-12 23:13:03.994032 by (mod) -

David

As long as you can keep the required line pitch (slope) of 4% and meet required property setbacks etc. I don't think you'll find an explicit distance limit. The D-box can be quite a distance away.

On 2018-02-12 23:03:18.085829 by David

How far can a d box be from the septic tank. My tank has two lids

On 2017-10-31 17:21:08.350319 by James

Is a D box supposed to be level

On 2017-09-19 12:29:53.666441 by Vin

Dbox isn't full of waste water, but instead water level is at or below leach field pipes. Dosen't this suggest that the system is working properly?

On 2017-07-18 14:25:30.014053 by John

Is there a certain way that the lines need to be connected to the box, or just glue the in?

On 2017-07-13 22:03:36.100687 by (mod) -

Nell

Pretty-much yes, A d-box or equivalent would be needed to permit branching out of the effluent distribution lines, unless there were only a single drainfield line.

On 2017-07-13 12:53:24.419484 by Nell

Do all trench type systems require using s "D" box? House located on a hilly property

On 2017-05-11 18:15:13.742568 by (mod) -

Dalton,

Thank you for asking an important question about stuck d-box coverage.

It would be almost impossible for there to be a suction pressure that would be holding a d-box lid in place. More likely a previous installer used a sealant or caulk to seal the lid against ground water leaking into the system. You may be able to pry the lid off by working carefully with a thin flat bar.

On 2017-05-11 17:30:58.775908 by Dalton

We have located our D box but the lip is sealed tight and we cant take the lid off. Any ideas to release the pressure

On 2017-05-08 22:58:39.366440 by Ken

How much does it cost and replace a d box

On 2017-04-19 20:28:18.978981 by (mod) -

A flooded failing drainfield

On 2017-04-19 13:18:03.873706 by Mark

I'm buying a house and found that the Septic System failed inspection do to water in the D-box. What are some or a reason that the D-box would get water in it?

On 2017-02-11 18:08:27.228809 by (mod) -

Home

Distribution boxes have been installed on septic systems for more than 100 years, depending on the septic system design.

A septic design might not use a D-box in some installations even if the installer built a network of multiple leach lines.

However regulating the flow among those lines would be then impossible, and the construction of such a system is more-difficult as the proper slope has to be carefully maintained.

On 2017-02-11 13:32:10.525479 by Homebuyer

Does anyone know when d-boxes started to be installed in homes in VA? For instance a house built in 1975, could it possibly be without a d-box?

On 2016-08-20 19:03:26.121493 by (mod) - comparing height of inlet and outlet openings in septic tank and D-box

AT THE DISTRIBUTION BOX:

the inlet should be higher than the outlet openings in the D-box.
Otherwise the D-box has to flood before wastewater flows to the soakbeds.

Because only effluent, not solids, should be in the line between tank and D-box, this problem is not as critical as a backwards-plumbed septic tank (I'll describe that too in a moment).

Typically we see adjustments in the D-box to permit balancing of effluent flow among various leachfield (soakbed) lines or even to rest some of those laterals by shutting them off from time to time.

As long as the effluent is flowing freely into the soakbeds you're probably OK.

But if the D-box has to flood to its rim before it pushes effluent out to the fields then the septic tank may be back-flooding and not working properly itself.

For other readers:

AT THE SEPTIC TANK:

The septic tank outlet is normally higher than the tank inlet. If a tank is installed "backwards" as we sometimes find, it will not work properly.

For effluent to rise high enough to exit the backwards-plumbed septic tank to the absorption fields or soakbeds through the higher tank's inlet opening, the incoming wastewater, entering through the lower "exit" opening, will have to rise above that opening.

That tends to leave solids in the waste piping between building and tank and can result in a sewage backup in the building.

On 2016-08-20 by Dee - gurgling from our bathroom closest to the septic

We are hearing gurgling from our bathroom closest to the septic; we opened the D-box to inspect, there are no clogs but noticed the inlet from the septic tank is lower than the outlets to the field. This doesn't seem normal but is it a problem?

On 2016-04-21 17:25:31.632049 by (mod) -

Tina I actually don't think one product is better than the other, though the plastic or fiberglass D-box might have better built-in seals around connecting pipes while the concrete box might require application of a sealant. (no big deal)

On 2016-04-20 21:24:58.547115 by Tina

We are having to replace our leechfield and D Box. It's replacing a 50 year old system. The box is concrete. What is the difference between the concrete box and the plastic box. Which is better?

On 2016-04-10 20:35:44.408942 by (mod) -

If the box is intact I'd replace the bad lid.

On 2016-04-10 18:42:08.284233 by Denny

Hi,
I have a concrete d box with a plastic d box on the inside of it. The concrete lid was cracked and starting to crumble. the rest of the concrete box looks ok and its lined with a plastic d box (Is this normal?) Should I replace the whole thing or just in stall the refabricated lid?

On 2015-01-20 21:06:30.786760 by (mod) -

Gillian and others, please Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies

Question: Repairman says hard water will ruin my water treatment system and drainfield

I have hard water and treat it with a culligan system. My neighbor had a title five and needed to have his D-box replaced to pass. The repairman said the whole street will have the same problem because of hard water will my treated water system help or hurt my system - Kevin 9/29/12

How do they test for Title 5?

Reply:

Kevin,

Water softeners, installed to improve water that is too high in mineral content, do not specifically attack D-boxes, but an improperly adjusted softener can increase salt dose into a drainfield, impacting its function and life, and a softener stuck in backwash mode can flood the field.

And it doesn't quite make sense to me for your repairman to say that hard water will damage your water softener. The purpose of the water softener is to treat hard water. That's its job.

Search InspectApedia for

Water Softener Impact on Septic Systems

to read the details.

If you search InspectAPedia for

Massachusetts Septic System Testing Law

you'll find a discussion of the law, specifications, and test procedures. It's more than a "test" - involving site inspection, history, water table depth, etc

Question: how often should the soakaway bed / septic field distribution box be checked?

(July 15, 2014) Anonymous said:
at what age should the distribution box be inspected.

Reply:

Good question, Anon, for which I've not found an authoritative answer for these reasons:

OPINION: The need for & frequency of inspection of the D-box would vary by septic system design, local soil properties, level of usage.

For example in a system design that uses manually-set alternating soakaway bed field trenches the frequency would be at least that of the planned swap between fields - perhaps every 5 years.

Most people ignore the D-box and never look there until there is a sign of trouble. Then the box is located, opened and inspected for evidence of the septic field condition.

That's when defects such as tipping, leaks, or uneven outlet distribution are more likely to be discovered.

If I were to propose a D-box inspection frequency I'd suggest

1. Inspect any time there is other evidence of a septic system backup, failure, or effluent breakout

2. Inspect the D-box on a frequency specified by the septic system designer - if any was specified. For example alternating bed septic systems that use a pump or siphon system may specify annual inspection to check for equipment malfunction or for adjustment.

3. Inspect at the frequency of required drainfield area exchange / rest / modification

4. Inspect at 5-10 year frequency in other conditions

Question: sewage does not flow uphill

(Aug 25, 2014) Charlie said:
Hi, while digging a trench I accidentally broke the main septic line between my Septic Tank and D-Box. The pipe was schedule 20 4" septic and was oblong. The pipe between the break and the D-Box was full of sludge. Also found out lid on D-Box was broken so it was plugged solid with dirt. I suspect this happened about 3 months ago while I was rototilling.

Was able to clean everything out and fix the broken line, however discovered that the D-Box is actually uphill from septic tank. It also appeared that the pipe was possibly cracked even before I hit it. Their was a lot of black soil underneath the break. My guess is it happened 10 years ago when the original irrigation system was put in.

I know the tank is not full, so my question is what caused all the sludge build up in the pipe? Was it cracked pipe, the uphill grade, or the plugged D-Box?

Reply:

Charlie

Oh for pete's sake: who the heck put the D-box uphill from the septic tank? The proverbial expression is "S_it doesn't flow uphill"

That would leave sludge in the pipe.

Question: flooding seen at the D-box

(Jan 6, 2015) Jamie Steele said:
Ok, i had a back up into my house. I had a company come out and pump the septic tank out (which was full of solids). They mentioned that they thought the distribution box might be clogged as well.

So a couple of days later we dug up the d-box. When we got to the lid on the dbox a hole accidentally was knocked into the lid and water started coming up from the dbox (the lid subsequently fell apart so a new had to be made). We pumped the dbox out but there were no solids in the dbox.

We snaked the line from the septic tank to the dbox as well as both distribution lines and found no blockages of any kind.

Then 3 days of solid rain hit the area and we basically pumped on a regular basis to keep the hole from filling up with water.

Now we have the lid finished but not installed back on the dbox. Is it normal in this situation, with the lid not on the dbox, for water to keep coming up from the dbox. Or is it a sign of another issue?

Reply:

Jamie

What you describe is an illustration of why pumping a septic tank will not fix a septic backup problem.

All it does is buy some time - until the tank is filled again, which could be hours or days. The backflow out of the D-box shows that the drainfield is saturated = flooded - not working.

Question: solids in the D-box or septic distribution box

20 January 2015 Gillian Andrew said:
I

have a gravity operated septic system under 6 years old. I had the tank pumped a few weeks ago because I'd noticed water making the driveway stay wet much longer on one side after heavy rain, nearest the septic field, and starting about halfway down it, about run 2 or 3 of 4.

The tank was full. But the problem is still present, so I uncovered the Distribution box to inspect it for the first time. It has flow levellers.

There is opaque dark brown liquid up to or close to the hole in each leveller. It looks scummy. There is no smell. Is there a problem?

Reply:

Gillian

In normal conditions a septic tank is always "full" - to the bottom of its outlet pipe. Pumping won't fix a thing though it may give a few days of relief.

If the drainfields are flooded the system needs replacement or repair or surface water or runoff diversion away from the soakaway beds.

If the D-box is full above its outlet levelers that's another clue that the fields are saturated.

If the D-box contains solids that's more disturbing news as it suggests that the septic tank outlet baffle is damaged or lost. Pushing solids into the soakbed significantly shortens its further life.

Question: my 30 year old septic has never given trouble, but has no D-box - Massachusetts says I need one. Really?

(May 20, 2015) Anne MacAdam said:
My Septic System was built in 1986 as specified in Engineering Title 5 Drawings. A D Box was specified between the Tank and A Leeching Tank.

Now I am trying to sell my Home of 30 years, and find that no D Box was provided.

The articles here indicate that the D Box is primarily a distribution System to serve a Leeching Tile Field of multiple lines. Why is a D Box required in a system that has never given me a single bit of trouble?

In Massachusets, I can not sell my home unless I tear up my New Driveway to put one in between Septic Tank and Leeching Tank. Please Help explain Law.

Reply:

Anne,

"never given trouble" does not mean that sewage effluent has been properly disposed-of nor treated nor that it has not contaminated the environment.

More likely it means there was no visible problem at the ground surface. The features of a D_box and and why they are used in the article above.

For example the D-box allows both the distribution of effluent over several different soakbed trenches and it permits the balancing of that flow. It also gives a viewpoint to determine the condition of the fields, for example to see if there is a backup or an imbalance in flow.

The cost of repairing building defect such as a missing D-box is first, trivial as a percentage of the value of a home, less than one percent of the home's value in almost any imaginable circumstance so certainly should not get in the way of completing a sale,

and second, I'd worry that a system that was improperly installed in the first place might have other more costly but hidden problems.

Better to know that up front than to have a costly surprise or fraud litigation down the road.

If any of the articles in this series are not clear I'd be grateful for a specific question and I'd be glad to research or reply further.

Question: D-box ahead of the septic tank?

(Jan 19, 2016) scott said:
my tank has a d box attached to the tank before the sewage enters. Is there a reason for that.

Reply:

Scott

Possibly to accomodate future additional sewer line connections or to give a cleanout access.

Question: replace just the D-box lid?

2016/04/12 Denny said:
Hi,
I have a concrete d box with a plastic d box on the inside of it. The concrete lid was cracked and starting to crumble.

the rest of the concrete box looks ok and its lined with a plastic d box (Is this normal?) Should I replace the whole thing or just in stall the refabricated lid?

Reply:

If the box is intact I'd replace the bad lid. Be sure it's water tight.

...

Continue reading  at SEPTIC D-BOX INSTALL, LOCATE, REPAIR - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see this

Septic D-Box Article Series Contents

• SEPTIC D-BOX INSTALL, LOCATE, REPAIR - home for septic distribution box, drop box, D-box
  • SEPTIC D-BOX COVERS - cover leaks, cover sealing, cover safety at the septic system distribution box
  • SEPTIC D-BOX FLOODING - causes & cures for flooding & leaks at the septic system distribution box or Drop Box
  • SEPTIC D-BOX INSPECTION - How to inspect the septic system distribution box for clues of septic drainfield condition
  • SEPTIC D-BOX LOCATION - how to find the D-box
  • SEPTIC D-BOX PIPING - solid vs. perforated piping
  • SEPTIC D-BOX SPECIFICATIONS - sanitary code examples of D-box requirements
  • SEPTIC D-BOX SPLITTERS - Using a D-box control or a Splitter Valve for drainfield resting & restoration
  • SEPTIC D-BOX TEMPORARY REPAIR - temporary repair bypassing the Drop Box may work in a few cases
  • SEPTIC D-BOX TROUBLESHOOTING - simple repairs at the D-Box can improve septic drainfield performance and may eliminate a Tipped D-box, Distribution -Box Leaks, Drop Box Odor

Suggested citation for this web page

SEPTIC D-BOX INSTALL REPAIR FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to SEPTIC DRAINFIELDS & D-BOXES

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