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

  • SEPTIC D-BOX TROUBLESHOOTING - CONTENTS: signs of septic system trouble that show up at the drop box. Simple repairs at the D-Box can improve septic drainfield performance and may eliminate septic odors. Tipped D-box, D-Box Leaks, D-Box Odors
  • POST a QUESTION or READ FAQs about septic system D-box installation, inspection, troubleshooting, and repair or replacement
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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.

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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


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:

  • 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 (SEPTIC TANK PUMPING SCHEDULE) and that the baffles are in place and working. (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. At also see SEPTIC TANK INSPECTION PROCEDURE, and SEPTIC TANK INSPECTION PROCEDURE, and finally, see Septic Tank Leaks.

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.

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.


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