Septic distribution box inspection - US EPA Septic System D-Box
Install, Inspect, Test & Fix Septic System Distribution Box

  • SEPTIC D-BOX INSTALL REPAIR - CONTENTS: Septic system distribution boxes - drop boxes: How to find the septic drainfield D-box - septic distribution box, D-box installation, specifications, design, leveling, adjustment, troubleshooting & repair. Simple repairs at the D-Box can improve septic drainfield performance and may eliminate septic odors. Using a D-box control or a Splitter Valve for drainfield resting & restoration
  • POST a QUESTION or READ FAQs about septic system D-box installation, inspection, troubleshooting, and repair or replacement
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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.

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?

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Septic System Effluent Distribution Boxes: the D-Box

Photograph of  a modern concrete distribution box - in this case, stacked up at the manufacturing facility in Kingston, NY

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.

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Article Series Contents

How to Find the Septic System D-Box

Sketch of the septic system drop box or D-Box - US EPA 1980Question: 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

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Reply: Distance from the Septic tank to the D-Box:

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:

- running a snake or probe from the septic tank outlet until it stops will give the distance to the D-box (probably)

- look for a depression in the ground a couple of feet in diameter and between the septic tank and the drainfield.

- 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.

See SEPTIC DRAWINGS for some sketches that give an idea where the distribution box is typically found

D-BOX Specifications & Code Requirements

Septic system D-box or drop box layout in the septic system - US EPA 1980The 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.


Continue reading at SEPTIC D-BOX INSPECTION


INSPECTING THE D-BOX - Inspecting the Septic System Distribution Box

Septic D box in trouble (C) Daniel Friedman N DayThe 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 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 are now at 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

Reader Question: water is leaking out of my distribution box. Should the lid be sealed?

Reply: Details about flooding, leaks and odors at the drop box are now at SEPTIC D-BOX FLOODING

Distribution Box Cover Troubleshooting & Repair

Question: How to repair a bad D-box lid or cover

My D box lid has failed and the sides are starting to crumble.

Reply: Details about septic drop box covers have been moved to SEPTIC D-BOX COVERS

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

Reader Question: My d box is damaged, can I just eliminate it and plumb directly to the leach field lines?

Reply: yes but just in emergency - it's better to replace and set the D-box properly.


Septic System D-Box Splitters - Drainfield Resting

Reader Question: What's the difference between a septic system D-box and a Splitter?

Reply: Basically there is no difference in function between a D-box and a Splitter box.

For details about drop box splitters and drainfield resting and recovery or Drainfield R&R approaches see SEPTIC D-BOX SPLITTERS


Continue reading at SEPTIC D-BOX INSPECTION or select a topic from the More Reading links shown below.

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