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.

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

Tipped Distribution Box

ipped 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:

We 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:

• At left: the down-facing elbow marks the effluent inlet to the D-box. The elbow is intended to prevent effluent from short-circuiting through the box to the opposing outlet. The downward pointing effluent promotes even flow through the box and into the two outlets.

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

• We can see at least two effluent outlets, at the photo's top and bottom. There could have been a third outlet at the right end of the box - one can't quite see for sure. If you look closely at the photo [click to enlarge this or any InspectAPedia image], you can see the teeth on the adjustable outflow limiter, which is installed almost flush with the box wall.

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.

 

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.

...

---

---

ADVERTISEMENT

---

---

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

How much floating solids should be in the Septic Tank Distribution-box?

How much floating solids observed with the effluent draining into the distribution box is normal?

There is a consistent small amount coming in to my d box and I’m wondering how much is too much?

By the way the video that I included is after I had flushed out and cleaned the distribution box which had or appeared to have a significant amount of solid matter accumulated in it. The last time the box was pumped was 2006. Thanks On 2022-06-06 by Mike

by InspectApedia-911 (mod) - None! there should be no solid waste found in the D-box

@Mike,

There should be no solid waste found in the D-box, just clarified effluent.

If you're seeing bits of toilet paper, feces, etc. in the D-box then the system is backing up and in failure. The problem is that when solids pass out of the septic tank and into the D-box they enter the drainfield and clog the soil, ultimately causing field failure.

Regular pumping extends the life of the septic soakaway or drainfield, but it won't fix an already-clogged, failing field.

Start with an inspection of the septic tank for

• abnormally high sewage levels ( a blocked line or a failed drainfield)
• a damaged or missing baffle at the septic tank outlet

What to do about a soft or crumbling concrete septic D-box

My distribution box has not failed it has 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 2021-02-24 by Jacob

Reply by (mod) - replace it

@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.

Does a "deeply-buried" septic D-box mean that there is something wrong with the septic system?

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 locate 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 2021-01-19 by AImee

Reply by (mod) - warning about the implications of a deely-buried septic distribution box

Almee

The depth of the D-box is determined by the slope necessary to get the septic tank to drain (by gravity) to it (1/8" to 1'4" per foot of horizontal distance). So the d-box depth alone doesn't mean that the system is presently in "failure" BUT

Watch out: 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);

Could a septic D-box become clogged?

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 2021-01-18 by Dave

Reply by (mod) - yes but that means the septic drainfield is in question or has failed too

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

What's the significance of low liquid level in the septic D-box?

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 2020-10-29 by Chris

Reply by (mod) - Clean and inspect the D-box for damage or leaks and replace it if needed

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.

...

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

Or see SEPTIC D-BOX INSTALL REPAIR FAQs - questions & answers posted originally here.

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 TROUBLESHOOTING 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

Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia

...

Ask a Question or Search InspectApedia

Share this article: