A septic D-box or "Distribution Box" is a small container that connects septic effluent pipes: an incoming wastewater pipe coming from the septic tank enters the D-box and the sewage liquid is then routed to one, or usually several outgoing effluent dispersal pipes that form the septic drainfield or soakaway bed.

In sum the D-box is a "junction box" for routing septic effluent into a drainfield.

Here we give eptic system D box installation, specifications, inspection, diagnosis, and repair, and we explain how to find the septic distribution box, drop box, or D-box by any of several methods.

We also provide links to additional details about how to inspect and repair the D-box if that's needed.

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

This series of septic system installation, maintenance & repair articles discusses the Inspection and Reporting the Condition of Private Residential Waste Disposal Systems - or - Where Does it Go When I Flush? and ... Will We Meet Again?

Septic System Effluent Distribution Boxes: the D-Box Home Page

Definition of a Septic D-Box: a septic distribution box is a container used to receive septic system effluent from a septic tank and to re-distribute the effluent into a network of attached drain-field or soakaway bed absorption trenches & pipes.

The D-box works by gravity, flowing effluent into the drainfield (or leachfield) piping network.

Our photo shows a stack of concrete drop boxes or distribution boxes at a local septic system supplier.

[Click to enlarge any image]

How to Find the Septic System D-Box

Question: distance from the septic tank to the D-box?

How far away from the septic tank is the dbox? - Kristin Clary

How far from the main tank is the D box located on average? - Fishass

[Click to enlarge any image]

Reply: Distance from the Septic tank to the D-Box gives a clue to the D-box location

Kristin & Fishass:

There is not a fixed distance from the septic tank to the distribution box; rather, its location depends on the space for and layout of the septic drainfield.

But you can often get a fair idea where the D-box is likely to be by any of several means:

1. Look for a depression
   
   in the ground a couple of feet in diameter and located between the septic tank and the drainfield.
   
   The D-box is normally not very deep, often between 6" and two feet to the top of the box.
   
   You may also see a pattern of parallel depressions, typically about 5 feet apart, that mark the individual drainfield leach lines. The D-box will at or near end of the drainfield area that is closest to the septic tank.
   
   More details about how to find the drainfield itself are in this
   
   Separate article: SEPTIC DRAINFIELD LOCATION
   
   Also at SEPTIC VIDEOS we walk a site showing you how to rule-in or rule-out various locations that would or would-not be expected to contain a drainfield, septic tank, or D-box
   
2. Look at the site layout
   
   for where the D-box could possibly be located.
   
   For example, if the drainfield site is level and rectangular, the D-box would typically be at or near the edge of the drainfield closest to the septic tank.
3. See if you can find a site plan
   
   or septic drawing that would have been filed when your septic system was approved by your local health or building department
   
   See SEPTIC DRAWINGS for some sketches that give an idea where the distribution box is typically found
4. Measure the distance to D-box:
   
   Run a plumbing snake or probe or sewer line camera from the septic tank outlet until it stops will give the distance to the D-box (probably)
   
   Once you know the distance to the D-box you have an arc along which the D-box will be found.
   
   The arc has its origin at the point where you inserted the plumbing snake into the effluent line, such as at the septic tank outlet baffle or tee, and the distance is what you measured when you withdrew the snake from the line after it was stopped by hitting the D-box.

Above: by inserting a sewer line camera or plumbing snake into the effluent line at the septic tank outlet baffle or tee you can measure the distance from that point to the D-box. The snake or camera will stop when it hits the D-box interior.

Then you can first inspect (for a depression) or if necessary, use the same snake, camera, or simply a tape measure to mark out the ground surface the arc along which the Drop box or D-box must lie. Some careful exploratory digging along that arc will find the distribution box.

Shown above: Ditch Witch 910 receiver used for locaing buried pipes and drains.

5. Use an electronic buried drain line locator to find the D-box
   
   A combination of a metal snake inserted into any buried pipe or drain line and special locating equipment (basically a metal detector) can find the exact route and location of the buried effluent line between the septic tank and the D-box.
   
   Just follow the buried line, using your locating device (and metal snake inserted into the buried effluent line) to its end and there you'll find the D-box.
   
   Details are at DRAINFIELD PIPE LOCATION, PRECISE where we also give sources of buried drain locating equipment.

 

Not All Septic Systems have a Drop Box

Above we describe finding the D-box for a septic system by several means. But is a Distribution box always even present?

Usually.

Really? Well not always. Most septic systems using a drainfield or absorption field or soakaway bed will have a D-box but not all of them. Some septic systems, particularly smaller capacity ones may use just one effluent distribution line. There will be no d-box or drop box on a single line effluent dispersal system.

What about mound septics and peat septics and aerobic septic systems? All of those systems that disperse effluent through more than a single dispersal pipe or line will use a form of drop box or D-box.

D-Box or Drop Box Specifications & Code Requirements

Watch out: as you'll note in our drawing, there may be multiple Distribution Boxes in some septic system designs.

The following building code example specification for septic system distribution boxes is excerpted from SEPTIC DISTRIBUTION LINES, BOXES, TYPES, NYS-A.7 Effective Date: 12/01/90 Title: Appendix 75-A.7 - Distribution devices

(1) Distribution Box Design Specifications - the D-Box Specs

(i) For accessibility, it is necessary that the distribution box be located and have a removable cover not more than 12 inches below grade.

Where, due to site conditions, a distribution box must be greater than 12 inches below the surface, an extension collar shall be installed to within 12 inches of the surface.

(ii) All outlets from the distribution box shall be at the same level to insure the even distribution of flow.

(iii) To minimize frost action and reduce the possibility of movement once installed, distribution boxes must be set on a bed of sand or pea gravel at least 12 inches thick.

(iv) The drop between inlet and outlet inverts shall be at least two inches. A baffle is required at the inlet side of the box when the slope from the septic tank to the box exceeds 1/2 inch per foot or when siphon dosing is used.

(v) There shall be a minimum two inch clearance between the inverts of the outlets and the bottom of the box to prevent short-circuiting and reduce solids carry-over.

(vi) Distribution boxes may be constructed in place or purchased prefabricated. When concrete is used to construct boxes, it shall have a minimum compressive strength of 2,500 psi at 28 day set.

(vii) Prefabricated boxes may be constructed of concrete, fiberglass, or plastic. The boxes shall be installed in conformance with the manufacturer's instructions in addition to the requirements above.

Inspecting the Septic System Distribution Box

The distribution box (more than one may be in use) connects a single effluent line from the septic tank to a network of absorption system components such as drainfield leach lines or to a network of seepage pits or galleys.

Details are now found

at SEPTIC D-BOX INSPECTION

Septic D-Box Piping

Question: are the pipes from the D-box solid or perforated?

Reply: It depends on septic drainfield layout.

Details have been moved to

SEPTIC D-BOX PIPING

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

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

Reply: Details about thorough inspection and diagnosis of Drop box problems are now

at SEPTIC D-BOX TROUBLESHOOTING

Distribution Box Clogs, Flooding Leaks & Odors: troubleshooting & repair

Details about flooding, leaks and odors at the drop box are now

at SEPTIC D-BOX FLOODING

Distribution Box Cover Troubleshooting & Repair

Details about septic drop box covers have been moved

to SEPTIC D-BOX COVERS

Temporary D-Box Repairs - eliminate the D-box?

Details are now at SEPTIC D-BOX TEMPORARY REPAIR

Septic System D-Box Splitters - Drainfield Resting

For details about drop box splitters and drainfield resting and recovery or Drainfield R&R approaches

see SEPTIC D-BOX SPLITTERS

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2022-10-02 by Martin - Where to find a replacement for the D-box and what size to order - does the new D-box size have to match the original?

My distribution box is (was) concrete and 12"x36", and only the bottom remains.

It has 1 inlet and 3 out. I cannot find a similar distribution box anywhere online.

Does it have to have the same dimensions or can I use any size as long as it has at least 1 inlets and 3 outlets?

Reply by InspectApedia (Editor) - replacement D-box must have correct number of inlets and outlets

@Martin,

It's perfectly fine and functional to replace your old D-box with one that is larger or even a bit smaller as long as it has the correct number of inlets and outlets, but if you can find one whose dimensions make connecting to the existing sewage inlet and outlet ports easiest, with minimum additional digging and re-piping, the D-box replacement job will be easier, faster, and much less costly.

So make a plan-drawing giving the dimensions and arrangement of piping and take that to D-box suppliers to see what fits best.

On our example sketch below you'll notice that dimensions A, B, C, and D are more-important when replacing a D-box than dimensions E and F **if** we don't want to have to make lateral relocation adjustments of the incoming and outgoing septic effluent lines.

 

On 2022-06-11 by Big John - Will pouring a treatment into our septic lines restore the septic system and Distribution box?

My septic system was installed in 2007. It includes a distribution box and two drain fields approximately 80 ' in length. All went well until recently. The toilets, shower and sinks began to drain slowly and after a few days began to back up.

I had the tank pumped and was told there were roots present inside the tank that needed to be treated as well as the drain fields and copper sulfate was recommended. Since the initial problem was resolved I was in no hurry to follow up on the recommendations. ( bad decision )

About 7 weeks water was discovered over and about the distribution box. I poured 2.5 - 3 lbs of copper sulfate down an access pipe into the distribution box hoping this would eliminate any invading roots and hopefully cleanse the media below the drain field permitting it to function properly again.

Well, this hasn't solved the problem as yet. Yesterday while mowing grass I noticed sewer water bubbling out of the ground again.

My question, after 14 years of neglect is it reasonable to expect a treatment poured into the lines to restore its ability to function again? Your answer and suggestion will be greatly appreciated. Big John.

Reply by InspectApedia (mod) - invading roots in septic field - treatments won't work

@Big John,

Thank you for the helpful question.

In more than five decades of work on septic systems I've never found a single instance in which pouring anything down a drain fixed a failed septic system.

Details are at SEPTIC TREATMENTS & CHEMICALS

Even if you use mechanical cleaning to route out the drain lines, the area around them is filled with invading roots, and quite possibly the soil is clogging your drain field.

Before launching into an extensive replacement of the fields, it might be worth sending a sewer line camera down each of the septic field drain lines to see their condition.

 

Will a little sand falling into the D-box during installation be a problem?

Hello,

Is it dangerous for my septic system if a small amount of sand enters my distribution box while it is being buried? My system will be completed in a few days, and the concrete lid has a little bit of play side to side. I'm the homeowner and just curious if this is grounds for concern. Thank you On 2022-05-07 by Tom -

Reply by Inspectapedia Com Moderator (mod) - sand in septic system

@Tom,

If by "small amount of sand" you mean a sprinkling then it's harmless.

If so much sand enters the d-box that it could clog or block one of the lines, that would be a concern.

 

Water marks in septic D-box led our inspector to faile the septic system - is that reasonable?

Can an inspector fail your septic, because there are watermarks above the outlet but no actual water at the time of the inspection. On 2022-01-27 by Gary Phillips -

Reply by Inspectapedia Com Moderator (mod) - signs of a flooded D-box

@Gary Phillips,

Certainly signs of a flooded D-box are at the very least a warning that there has been a failure in the past. Additional clues that an inspector might find may permit her to form the opinion that the signs of prior drainfield failure are accompanied by no evidence that a prior problem has been corrected, thus that the condition is still there.

Keep in mind that a septic drainfield may flood or be in failure mode episodically rather than continuously, as weather and usage and other conditions vary. The fact that we "only sometimes " send our sewage into the environment, into nearby waterways, or potentially into people's drinking water wells is still a septic failure that needs to be addressed.

In my OPINON, an inspector who failed to issue a septic failure warning if there are signs of septic system flooding would not be doing her job.

 

Are there septic D-boxes made of plastic?

Are there plastic D box manufactured

On 2021-05-07 by William -

Reply by danjoefriedman (mod) - plastic and fiberglass septic D-boxes available

@William,

Yes there are plastic, fiberglass as well as pre-cast concrete Septic D-boxes widely sold.

Below is an example, the Tuf-Tite 9-hole Septic D-box that sells for about $75. U.S. (in a size for 4-inch effluent lines)

What is the square box we found about 100 feet past our septic tank?

Looking for help on 11 year old mystery of (dry well) Have septic and about 100 feet past the clean out. is a square box in ground with lid old owner told us that was from the 50's when they could send laundry water to that...they added up pump to send laundry to sump when I bought. (code) It was dry for 5 years now all of a sudden it stays FULL

I drained it to see whats down there and there are 3 tubes? Not 2 like one would think (one in from house and one out) one also in corner to S neighbor. I have never had septic until now so all new to me. Any help would be great :) On 2020-06-04 by ms.sparty

Looking for help on 11 year old mystery of (dry well) Have septic and about 100 feet past the clean out. is a square box in ground with lid old owner told us that was from the 50's when they could send laundry water to that...they added up pump to send laundry to sump when I bought. (code) It was dry for 5 years now all of a sudden it stays FULL

I drained it to see whats down there and there are 3 tubes? Not 2 like one would think (one in from house and one out) one also in corner to S neighbor. I have never had septic until now so all new to me. Any help would be great :) - On 2020-06-04 by ms.sparty

Reply by (mod) -

Sparty

From your description I think you are probably describing was called a d box or distribution box that is used to Route effluent from the septic tank into multiple drain field lines.

You can find more about the D box or distribution box in the index to related articles found on this page.

If the distribution box is filled with a fluid and not draining then most likely the lines to the drainfield are either blocked or the drain field has failed and has stopped absorbing effluent

 

Should the septic D-box inlet have a levler adjustment on it?

My septic system's 4-hole distribution box has levelers on all 3 outlets and the inlet. Should the inlet have a leveler on it?

All pipes are 4" but the leveler's hole is only about 1.5", effectively reducing the input line from 4" to 1.5". Is this normal? - On 2020-05-21 by Anonymous -

Reply by (mod) -

Anon

Thanks for an interesting question. I don't normally see a leveler on the inlet to a D-box.

If we consider what's supposed to be going-on, effluent should flow freely from the septic tank into the D-box and then flow out of the D-box to the fields, with distribution to individual field leach lines being balanced as needed among your 3 outlet openings.

Installing a leveler on the inlet to the D-box, in my OPINION, does nothing useful and could cause harm by restricting effluent inflow into the D-box and onwards to the soakaway beds.

The risks are clogs at the inlet side or even a septic tank backup.

 

Are these costs to replace my Distribution box reasonable?

Need to know following est to replace d box, $2115.00., permit, jetting. Plus disc $151.00 total $ 2,584.00. Is this reasonable? I am retired senior. Not familiar with standard costs. Thank u On 2020-04-27 by Nancy mc laughlin -

Reply by (mod) -

That sounds stunningly expensive, but we don't know your site so don't know just how much labor and machinery are required.

Can you get a second estimate from another company?

 

What's the maximum distance from septic tank to D-Box?

What is maximum length of line between septic tank and diverter box ? - On 2020-03-04 by David -

Reply by (mod) -

David

There's not a code-specified maximum distance between septic tank and the D-box, but there will be a technical or practical distance limitation since the main effluent line from tank to D_box and from D-box to absorption trenches has to slope (typically 1/8" to 1/4" per foot).

A very long run that pushes drainfield lines too deep will have you building a system that lacks soil oxygen and thus doesn't treat the effluent adequately (not enough bacterial action) so then contaminates the environment, groundwater, wells.

 

What's the life of a septic system Distribution Box?

I had some water in my basement while doing a load of laundry and called a sewage pumpout company who came in and emptied the septic tank.

It had not been pumped out since 2010. I live alone in the house. He thinks there could be a problem with the distribution box and wants to come back to locate it and inspect and, I assume, replace it.

I'm assuming the box is the original from when the house was built in either 1983 or 1986 and I've been here since 1993.

What is the usual life of a distribution box and how much should it cost to locate, inspect and replace? Thank you. v

Reply by (mod) - What is the usual life of a distribution box ?

Joyce:

If the Distribution Box is blocked or clogged you will have constant sewage backup into your home, coming up through the lowest drains in the house whenever you use a plumbing fixture.

Keep in mind that pumping a septic tank, while critical for septic drainfield life, will never ever fix a clogged drain nor a failed drainfield.

 

Tenant poured grease down my kitchen sink and put baby wipes and female products down the toilet

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 2019-05-06 by Carol -

Reply by (mod) - clogged D-box or effluent line

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.

 

Why won't grass grow near our septic system D-box?

We've lived in this house for more than 20 years and for most of those years we've had trouble getting grass to grow at and just down hill from the D-box.

Many years ago we had a swampy area there and when we had the tank vacuumed out we asked about that problem. They came back and pumped styrofoam pellets into the ground (I don't remember what the process was called and it may not have been styrofoam, but small white pellets similar to perlite).

That helped the whole system quite a bit for some years, but now, as I stated we have problems getting grass to grow in a larger spot than the soggy area (the previous owners had also put an above ground pool over 2 lines of the leach field and we were told at the time of putting the pellets into the ground that we also should remove the pool which we did).

Do you have any ideas why the ground near the d-box won't grow grass well? Last year we even dug up the area, removed some soil, replaced it with fresh soil and resodded the area. On 2014-07-05 by Katie -

Reply by (mod) -

Katie,

If the soil depth over a concrete cover of a septic tank or distribution box is too thin it may lack sufficient moisture to support grass growth.

 

Can't find my septic system D-box: is there a standard depth for septic distribution boxes?

I'm having trouble locating my distribution box, my county didn't require site plans when this place was built in the 80's, and now suspect I am failing to dig far enough down. Is there an average or maximum depth below the outlet pipe on the septic that the Dbox will be installed in? On 2014-05-30 by sc -

Reply by (mod) - no but here's how to figure out the depth of your D-box and where it's located

SC

The depth of the D-box will be somewhere between the elevation of the outlet of the septic tank and the top of the drain field pipes to which it connects. That's site dependent.

YOu might go to the tank, insert a snake into the outlet pipe until it hits an obstruction, then pull it out and measure that length.

Presuming it hit the D-Box that'll give you the distance along an arc extending from the septic tank outlet.

Or use a pipe locating tool to follow the waste line.

 

Septic leach field seems clogged - it's covered by mature trees and has been there since the 1970's.

Our leach field seems to be clogged. It's across the fence with heavy woods and undergrowth. Digging anywhere seems a monumental task.

Seems like the whole woods will have to be removed! This system may have been installed in the 70s. - On 2014-05-26 by Barbra -

Reply by (mod) -

Barbra

It does sound monumental, and expensive.

On the other hand, if your leach field is overgrown with woods and undergrowth chances are that its pipe system is quite invaded with roots, not working and thus needs replacement.

Modest exploratory digging is not a big deal but if you need to replace the fields you could not do so successfully amidst woodlands and heavy undergrowth anyway.

I'd review the site to see if there is a more suitable location. If not, $orry for the bad new$.

- Moderator

 

Is standing water on a small area of my septic drainfield a worry?

B.Ayers I have just noticed standing water on a small portion of my drainfield.Should I be worried? System is 15 years old. - On 2014-03-24 by Anonymous -

Reply by (mod) - yes; investigate further to diagnose the problem.

Unfortunately Anon, that suggests you should indeed be worried.

Either the drainfield is failing or surface runoff is flooding the field.

It's worth investigating further since if you're lucky there's a broken clogged pipe repair needed rather than a whole new drainfield.

...

Continue reading  at SEPTIC D-BOX INSPECTION 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 on this page

Or see these

Recommended Articles

• ALTERNATING BED SEPTIC SYSTEMS
• DRAINFIELD PIPE LOCATION, PRECISE - using electronic equipment to find buried pipes
• SEPTIC COMPONENT LOCATIONS
• 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 / Diverter 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
• SEPTIC DRAINFIELD LOCATION
• SEPTIC TANK, HOW TO FIND
• SEPTIC TANK LOCATING EQUIPMENT

Suggested citation for this web page

SEPTIC D-BOX INSTALL, LOCATE, REPAIR 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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