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Septic distribution box inspection - US EPA Septic System D-Box Problem Diagnosis
Inspect, Test & Fix Septic System Distribution Box leaks, odors, malfunction

Diagnose problems at the septic system drop box: procedures for troubleshooting leaks, smells, or backups & flooding in the septic system D-box.

Septic system D box installation, specifications, inspection, diagnosis, and repair: 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".

If the D-box is leaking, smells, or is tipped, clogged, or otherwise not working this article describes how to diagnose & fix the trouble.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Signs of D-Box Trouble, Advice on D-Box Repairs

Septic D box in trouble (C) Daniel Friedman N DayTipped Distribution Box

Reader Question: Tipped septic effluent distribution box, standing water at end of one leach line


I am being told that my D box is bad. When no levelers are in place all effluent runs into only one port.

I have been told that the way that fitting is angled down low and how it comes in angled is bad. It is making me worried. I am essentially being old that it should be redone.

We have Type III soils, very sandy with 2 - 75' long infiltrators.

Three years ago during the wet season I noticed some standing water at the end of one of the laterals.

It was the lateral that receives all the effluent when no levelers are in place. - Nicholas Day

Reply:

Septic D box in trouble (C) Daniel Friedman N DayWe were not sure from the two photos but the D-box looks small, and as if it has been invaded by sewage (suggesting the tank was not pumped on schedule or your tank baffles may be bad).

With thanks to clarifications from reader Doug (March 2013), we recap the effluent distribution piping connections to this D-box as follows:

Without the elbow, effluent flows more forcibly across the box and into the opposing outlet, but very little effluent will make the 90-degree turn into the perpendicular outlet. This is a very common installation practice

If you knew for example that one of your lines was much longer than the other, you'd send more effluent to the longer line - presuming they are both working ok.

As you report that one of the laterals showed a sign of failure during wet weather several years ago, you might want to try to re-balance the effluent flow sending more (or perhaps temporarily, most) of the effluent into the other drainfield line.

But to have an accurate idea of the condition of the drainfield sections or leach lines before adjusting the effluent flow in your D-Box, the best step would be to carefully excavate near the end of each of the two leach lines (presuming you don't already have inspection ports installed). Look at the condition of the soils there, particularly, look for standing water or effluent.

Because the D-box is a small thing and not deep, it shouldn't be a big job nor too costly to dig it out, install a larger one, make sure the D-box is not tipped, and that effluent is flowing as desired into both of the drainfield lines.

But you should also check the septic tank condition, especially the outlet baffle, and the scum/sludge levels, to be sure the tank is pumped on schedule and that the baffles are in place and working.

Details of septic tank pumping start

at SEPTIC TANK PUMPING SCHEDULE

To inspect septic tank baffle condition

see SEPTIC TANK BAFFLES

Another problem that could send sludge into the D-box would be a septic tank that floods from groundwater leaking into it, so you will want to check that too.

Also see SEPTIC TANK INSPECTION PROCEDURE,

and SEPTIC TANK INSPECTION PROCEDURE, and finally,

see SEPTIC TANK LEAKS since leaks into the septic tank can flood the D-box and drainfield or conversely, leaks into the D-box itself can flood the septic tank and drainfields.

Question: during a septic test the trenches "took on water" - they think the D box is kiltered. What does that mean and how do I fix it?

I had a Hydraulic Load test done and the trenches were taking on water...they think the D box is kiltered. Can you explain this and what are the recommendations to have it fixed? - Reen

Reply: a tipped d-box does not distribute effluent evenly among the drainfield lines and can cause flooded drainfields

Sure Reen: someone is making things sound like rocket science instead of simple ditch-digging.

A "kiltered" Dbox is lingo for a "tipped distribution box". As you can read above, the D-box is basically a plumbing junction box that receives incoming effluent from the septic tank and routes it out to multiple drainfield lines where the effluent can be further treated and absorbed into the ground.

If the D-box is "tipped" that means it's sending too much effluent down just one line (perhaps flooding it) and not enough effluent down other lines (not using them).

Also if surface runoff or ground water is leaking INTO your D-box, that water will add to the septic effluent liquid load and risks flooding and ruining the drainfields.

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-02-24 - by (mod) -

@Jacob, as the wise lady from Philadelphia tells us it's no use throwing good money after bad. It's time to replace that distribution box.

On 2021-02-24 by Jacob

My distribution box has not failed it is not lost its shape but the concrete of it has gotten soft is there anything to do that can harden that concrete back up

On 2021-01-19 - by (mod) -

Almee

You ask a fair question but not one I can answer very fully, as we have so little knowledge of your specific septic system;

Considering that the D-box normally drains to the drainfield by gravity, if it's so deep then that would make us ask "how deep is the drainfield itself? as a deep drainfield cannot possibly work properly to treat sewage pathogens (lack of oxygen);

On 2021-01-19 by AImee

Purchasing a house and the septic was replaced from gravity fed to pump in '03. Inspection found repairs needed were installing new risers and remounting the pimp control panel. What worries me is that the company is saying they could not locatte the distribution box due to the depth of it but after testing the systems saw no evidence of any failure. TO get to the distribution box it would require bringing in big equipment. - my question is is they common, should this be a red flag?

On 2021-01-18 - by (mod) -

Dave:

If the septic tank is pumped out (and the pumper really did actually pump out the tank),
and

if the septic system was then not in use for 3 weeks
and
if then on

inspection the tank is filled with liquid
then

there is either a leak of groundwater into the septic tank or its feeder piping,
or

the drainfield has failed and perhaps is itself flooded and is back-draining into the septic tank.

Those are, unfortunately bigger problems than would be explained by a blocked or failed D-box itself, though indeed if a D-box is topped or improperly set, it could cause field flooding and failure if it is not distributing effluent to all of the drainfield lines .

So there's nothing lost if you want to find the D-box and open and inspect it; let's do that, but be prepared for a failed field or back-flooding septic tank.

See SEPTIC D-BOX LOCATION - how to find the D-box

https://inspectapedia.com/septic/Septic_D-Box.php#Find

On 2021-01-18 by Dave

I bought a house that is about 50 years old. We bought it in August 2020 and started having issues in December.

Had the septic tank pumped on December 31st. We thought we had a clog in a line due to sewerage coming up into the bathtub.

Plumbers ran a snake and couldn’t find a clog. Another plumber ran a camera and found a possible blockage. They dug up outside and found a little compaction and cleared it. Also put in a clean out in the yard.

Didn’t use the toilet or drains for three weeks and lifted the lid to the septic tank and it was full of water.
Three septic installers said I need new drain fields. My neighbor is having a similar problem.

He’s putting a new d-box in. Could my d-box be clogged? The house sat empty for five years as far as we know. We had the home inspector run a dye test but now I know that’s useless.

On 2020-10-30 - by (mod) -

Totally baffling.

A D-box is simply a connector that routes effluent coming from the septic tank into one or more drainfield effluent disposal lines.

Replacing the D-box might involve some adjustment to balance the effluent load among the various output lines but I'm really surprised that the contractor thinks another septic loading test is needed.

Let's get around this arm-waving rave by going right to the approving authority. Call your local building or health department, find out if a permit and approval are even required to repair or replace a D-box, and if so (which would be surprising) ask exactly what you need to do.

Tell us what you're told and we can offer further comment or advice.

On 2020-10-29 by Chris

Please help. My 2 month vacant NJ house had a septic inspection by the buyers. They said the distribution box is leaking as ran water for 30 mins and then came back to check 2 days later and the level is 1" below operating level. (main field they said is fine) (I thought that they had run a hydraulic load test, or so it seemed to suggest in the report) Anyway we decided to go ahead and get box replaced but the septic guy we chose can't do the work as he is saying they didnt do a load test so he cant complete the work because a county representative wouldn't be able to sign off on the work!!!!

Is a hydraulic load test the only way to tell if a distribution box is leaking??? or can the leak be detected with a normal inspection. I am thinking of just getting my own inspection as this is a 2 week delay so far and we were supposed to be completing next week. (head slap) House has been empty since Sept 1st.

I wonder if the buyer and his septic company are trying to pull a fast one and get us to update something that isn't leaking???

On 2020-10-25 - by (mod) -

Inspection by camera has, fortunately, allowed you past speculative arm waving and into the world of moee useful facts.

The number of distribution boxes needed by a septic system varies and can range from one too many depending on the slope and shape of the terrain. So what you were told is perfectly reasonable.

What I don't understand and what is missing from what you've been told or were able to relate is the question of the condition of those distribution box is, why they all need to be replaced, and what the actual costs are.


That also varies by site.

Usually the main cost in replacing a distribution box is the cost of paying the excavator. So if a lot of Excavating is needed that msy expllain the cost.

Cost of the boxes themselves is small.

On 2020-10-25 by Ilana

I am told that I need to replace 2 distribution boxes; however, everywhere I look I am seeing that a septic tank only has one box. When the specialist came out the first time he told me he couldn’t find the D-Box. So he said he needed a special camera. He can out a second time and told me Dbox #1 is used to transport fluid to Dbox #2 and Dbox #2 has 3 outlets lines. That is when he informed me that both boxes need to be changed ($4300). Would love to understand if I am being taken advantage of, or if this is makes sense.

On 2020-08-20 by Anonymous

Thanks for your response. The backwards septic tank was unknown from 2004-2017. The septic system was inspected in 2017 which revealed the backwards tank. As a result, a new septic tank was installed the correct way in 2017 and the drains worked fine and the D box was not broke.

Three years later, the septic system was inspected again in 2020 resulting in the D-box broke and the drain lines not working. What would cause a septic system that was working correctly in 2017 to have a broken D box, and only one of three drain lines working when they were working 3 years ago?

On 2020-08-19 - by (mod) -

Jim

Unfortunately the report you give is oxymoronic insofar as it is self contradicting. A "backwards" septic tank cannot be operating properly as the inlet is lower than the outlet, pushing solids into and thus ruining the drainfield. Simiarly, a missing baffle causes the same trouble.

Jetting the fields in my OPINION and that of every reader who has reported trying that approach, gives at best short term relief for a failed drainfield.

On 2020-08-19 by Jim

The septic system was inspected in 2017 and found the distribution baffle missing and the tank installed backwards from when the house was built in 2004. Otherwise, the septic system was operating properly and had been since 2004 with regular maintenance. The baffle was replaced and a new tank was installed correctly.

Three years later in 2020, the septic was inspected again and found to have a broken distribution box, dirt in the D box, and only one of the three drain lines working. The inspector says everything needs replacing.

The county says replace the distribution box at the proper elevation, relevel the distribution laterals leaving the D box, and reinspect.

If needed have the laterals jetted (pressure cleaned) to remove any soil that may have infiltrated the broken D box. What are your recommendations and what are the expected costs?

On 2020-07-25 by Ann

Is it common for a septic systems D Box to need a filter

On 2020-06-23 - by (mod) -

If you eliminate the second 1000g septic tank in the basic front-end septic treatment system you will

- decrease the septic system capacity
- increase the frequency with which the septic tank needs to be pumped
- risk shortening the drainfield life by pushing solids into the fields

I would add a septic filter at the septic tank outlet
and
be sure that the remaining tank volume is adequate for the anticipated daily wastewater flow (even with increased pumping frequency)

If you don't check and do those things, the effective reduction in septic tank volume decreases the settling time in the tank and increases the push of small solids into the drainfield - killing the drainfield is an expensive mistake

Most important is that I don't hear anywhere in this that the actual problem has been properly diagnosed. If that's the case all of these steps are speculative and may be costly and ineffective.

A "D-box" does not commonly get overwhelmed by effluent inflow. The D-box is nothing but a junction box or splitter that divides up the incoming effluent from the tank and sends it out to two or more drainfield lines, giving a chance to balance flow among the lines.

If flow out of a D-box backs up then the problem is that the drainfield is failing or blocked or undersized and simply can't accept the incoming volume of effluent.


See SEPTIC TANK SIZE in the ARTICLE INDEX

On 2020-06-09 by Kevin F

Thanks for the response.

Agreed, I didn't really mean that I would get down in the tank, I would contract for that work if we went that route. I've had a contractor visit and he has checked and confirmed that we have enough slope to convert the existing pumped system to a traditional gravity flow system.

He proposes to abandon the second 1000 gallon tank that is currently used as the pumping tank, and instead add a new outlet to the 1st 1000 gallon tank which is the true septic tank. This tank is more accessible (not under the deck). The new outlet would go straight to the D-box out in the yard then to the 3 low profile chamber lines (each 90' long).

Any concerns with this approach? Is a 1000 gallon tank adequate for a 3-bedroom home? This gravity flow system would eliminate the current issue of the d-box being overwhelmed by too much flow too quickly due to holding for too long and then pumping too much at once. But not sure what new problems might come with this new plan (if any). Appreciate your thoughts.

On 2020-05-31 - by (mod) -

Kevin you could try further constricting the flow to the wet line - in the D-box. But it sounds as if you need a larger holding tank system and a timed dosing system to avoid overloading the fields - or, of course, more field capacity.

Watch out: DO NOT even think about getting into the septic tank; it's a quick death from methane gas; special equipment, a work partner, etc. are needed.

On 2020-05-30 by Kevin F

I have a positive pressure system in which a pump in the second septic tank pumps to a d-box and then to 3 low profile chamber drainfield lines, each 90' long.

My problem is that one drainfield line gets too much flow and we do see break through at the far end of the line in certain season and conditions. The other two lines seem healthy, no apparent issues, but they are getting water, just not as much

. All three lines out of the d-box have speed levelers and I've raised the level of the overly wet drainfield line but it still gets too much water. The reason seems to be that the pump rate is too fast and overwhelms the d-box such that it fills up and fills all line openings regardless of height.

So it's coming on two or three times a day and pumping a large volume of water at a fairly high rate into the d-box. It seems like we might do some good if we slowed down the rate of pumping and essentially had the pump come on more often, stay on longer and pump at a slower rate.

Then the d-box speed levelers come into play and truly limit flow to the overly wet line. Is this thinking correct? How can I slow the pump rate down? Would rather not have to get down into the tank to do this (its under my deck!), could you add a ball valve just before the d-box to choke the flow back a little (or is that a bad idea)? Any other thoughts or recommendations? Thanks in advance.

On 2020-04-26 by (mod) - My septic system was 1.5 years old when it failed w

All that sounds aggravating indeed as well as expensive.

It should be trivially easy to determine if a nearby spring is entering or sending water into your septic tank or drain field.

Particularly with a septic tank. You would have septic contractor open the tank and perhaps puppet and watch for drain back from any Source such as a saturated field or a leak into the effluent line leaving the septic tank or leak into the septic tank from anywhere. It would be good to do some diagnosis and be more confident about the problem before throwing more money at this topic

On 2020-04-26 by John

My septic system was 1.5 years old when it failed with 3 70 foot leach lines. Had it pumped several times and inspected. They think the system has a spring feeding it. I put that thought in their heads. Oops. They put in a new system that has a sump pump now to go up hill to the new 3 line 70 foot leach field. It failed after 4 months.

They put a French drain around my tank that empties out to another area thinking a spring is feeding my tank. No water coming out of the French drain and it’s been In for over a month. I have dampness in the dirt at the center leach field end.

That line fills first because it can be seen thru the inspection ports. The system is just about full again and will overflow from the tank, feeding the French drain and drain out to the surface. Has not happened yet, but I know it’s coming. I haven’t done laundry in months. I think it’s their cheap fix.

The line that feeds the center leach field is directly across from inlet from the sump pump in the D-Box. I think a 90 degree elbow should be installed facing downward to prevent the flow of water shooting directly into the center line. This way water would be evenly distributed.

I also think I need to extend my lines 20 or 30 feet each, or add a line. My soil just doesn’t leach. The second system is much shallower. I think they were hoping to rely on evaporation. I live in an area of CA that gets weather and fog during the winter months. Any thoughts?

On 2020-03-19 by (mod) - if one of your leach lines is flooding

Jim

Typically if one of your leach lines is flooding it's either blocked or the soil surrounding it has become saturated with ground water or the line is old and soil is clogged with a too-thick biomat.

Direct surface water away,
check the line for blockage (sewer line camera)
and if flooded but not by groundwater, close off the line pending replacement of the drainfield

On 2020-03-15 by Jim Rogers

I have a 3 line d box. One of the lines is bringing water to the surface at the end of the line, what would cause this problem and what fixes might I consider,

On 2019-08-26 - by (mod) -

While I agree that sanitary wipes or diapers should not be flushed down the drain and if they're going to septic tank they need to be removed, that's normally a part of any basic septic tank pumping and cleaning service. I can't imagine what extra work is being referred to but of course it's possible that there is something.

You septic pumper may not be an English major or clear communicator but the person not to be able to show you specifically what they're talkin about

On 2019-08-2 by Mary

I recently had my septic tank pumped. When the D-box was checked, I watched the pumper as he briefly stuck his hand into the box. He told me I had a broken pipe and that it was passing rocks. He also said it was tipped. He scheduled me for a drain field evaluation for $349.00. At first, I was stressed with worry about the outcome of all of this.

However, as I thought more about it, I'm now wondering if I'm being hustled. The pumper told me that there were sanitary products and baby wipes that had been flushed into the tank requiring him to do extra back washings. My adult daughter lives with me, but has never put these items down the toilet.

Question: The d-box is not distributing effluent evenly among my three drywells. Is it likely to be a tipped d box or a clog?

I have an old 3-drywell system fed from a d-box in the center of the 3 drywells (laid out on 3 points of an equilateral triangle).

The system has had minimal use but one drywell is full and the other 2 are bone dry. Should they all be being fed in parallel or in series (one fills before the next)? Is there likely a tip or a clog? - Jeff O

Reply: Drywells are often installed and fed in series; if yours are in parallel, set the D box to send effluent to all of them.

Often drywells were installed in series - not in parallel. If that's how yours were piped, then if you can confirm that the full drywell has an outlet pipe that drains into the next (dry) one in the series you should be OK. If that connection is missing I'd add it.

On 2019-08-26 by (mod) -

While I agree that sanitary wipes or diapers should not be flushed down the drain and if they're going to septic tank they need to be removed, that's normally a part of any basic septic tank pumping and cleaning service. I can't imagine what extra work is being referred to but of course it's possible that there is something.

You septic pumper may not be an English major or clear communicator but the person not to be able to show you specifically what they're talkin about

On 2019-08-25 by Mary

I recently had my septic tank pumped. When the D-box was checked, I watched the pumper as he briefly stuck his hand into the box. He told me I had a broken pipe and that it was passing rocks. He also said it was tipped

He scheduled me for a drain field evaluation for $349.00. At first, I was stressed with worry about the outcome of all of this. However, as I thought more about it, I'm now wondering if I'm being hustled.

The pumper told me that there were sanitary products and baby wipes that had been flushed into the tank requiring him to do extra back washings. My adult daughter lives with me, but has never put these items down the toilet.

On 2019-04-27 by (mod) - bottomless D-box

Concerned

That sound like an improper and un-sanitary and probably illegal septic system to me. Normally a D-box has an enclosed bottom just a few inches below the bottom of the inlet and outlet pipes.

And its overall dimensions are measured in inches or just a couple of feet.

If you're finding something much bigger it's not a D-box it's something else, maybe an old seepage pit.

On 2019-04-27 by Concerned Neighbor

The distribution box seems to lack a bottom. A long pole inserted goes way down below drainfield. System is located very close to Hood Canal, so effluent may be draining into Canal.

On 2018-09-14 by (mod) - leveling the D box

Mod replies:

Typically you'd shim the box level and assure the pipe connections are not leaking.

On 2018-08-05 by ted

any ideas on re leveling my existing distribution box. I only need to raise one corner.

On 2018-09-14 by (mod) - What we see in the D-box when tracking down a leak

On 2018-08-08 by John Va

Hi, I just dug up the pipe going from my septic to the D-Box, trying to find a leak (water coming out of the ground).

I found the pipe is ok, but the D-Box has collapsed. Black mud everywhere the D-Box should be. The only thing I could identify is the concrete bottom. The top and sides are gone. The pipes are still in place. I just had the septic pumped out and there was no sign of any sludge leaving the tank.

The D-Box may have been destroyed for years. It is in a part of the yard, that is never used and seldom mowed.

My question is, if I replace the D-Box, how do I clean out the field pipes (of mud) and test to see if they are ok ?
I was planning on cutting the output pipes back and then adding the needed pipe and coupler to get to the D-Box.

The pipes are pvc white pipe (not sure what schedule they are yet, or size (I believe 4", not measured yet)).
I just found the D-Box and it's condition an hour ago. I am sick over what I found and hoping I don't have to have a new drainage filed installed.
Any advice you can give will be greatly appreciated.

Also, I can get a plastic D-Box from nearby suppliers, but I will have to drive to another town to get a concrete box.
I am leaning towards getting the concrete box. What are your thoughts ?
(p.s. There are a lot of tree roots around where the D-Box is located. I am thinking they are what destroyed the D-Box.)

Thank you for your time.
John in Virginia

On 2018-05-12 by (mod) - Hoyt bat system leaks

Sounds like a blockage. I would open the d-box and take a look at what's going on.

On 2018-05-11 by Moricle27173@comcast.net

We just had anew Hoyt bat system installed.There is water coming out of distribution box area??

On 2017-08-07 by Matt

I have septic system that is about 10 years old. Within the last year, the d-box tipped and water was not flowing evenly through the pipes. I turned the levelers so that water would flow more evenly but the box has tilted to a point that one of the front lines still won't get even flow after making adjustments. How difficult would it be to dig up and level the distribution box itself, and can you provide any steps/tips for a DIY job?

On 2015-04-24 by Warren

I bought an old house that has a D-box which is essentially disconnected from the septic tank. The pipe from tank to D-box it is basically crushed, and the D-box is dry and looks like it was never used. (this is an old vacation home and never saw much traffic.)

I would like to just replace the 8' pipe from the tank to the D-box. Question: What kind of adhesive can I use to seal the pipes into place? The tank and D-box are both concrete and are in decent shape.

On 2015-04-21 by (mod) -

Jim

You could scope that way if there is an access port over the tank outlet - AND depending on the accessibiity given by the baffle. You could also use a snake to measure possible distances

On 2015-04-21 by Jim

can i camera scope my septic system from the discharge port of holding tank, with-out having tank cleaned out, as to find my d-box, we have no idea where it is, it is possible that it is under a stamped concrete patio laid well after house was built


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