Septic distribution boxes (d-boxes)

Septic distribution boxes: what we stock

Distribution boxes we stock, by brand and size

Hole counts and dimensions below come from the makers' data. Pick the box by the number of lines in the approved septic design, plus one inlet.

18" and 24" boxes are catch basins, not d-boxes

Tuf-Tite doesn't make an 18" or 24" square distribution box. The 18" and 24" square plastic boxes buyers ask for are NDS square catch basins, in a 4-opening model. They collect surface water from yards, driveways and downspouts. They have no built-in drop or level outlets to split septic effluent, so don't use one in place of a d-box on a septic job.

We stock NDS catch basins with grates for drainage work. See our NDS channel drain page for the catch basins and drains that go with them.

How does a septic distribution box work?

Effluent leaves the tank outlet, runs to the box, and leaves through the outlets at one level so each leach line takes an equal share. Tuf-Tite builds a 2" drop from inlet to outlets into its boxes.

Tuf-Tite says its polypropylene boxes set on level virgin soil with no concrete slab. Polylok lets the installer choose the inlet and outlet heights and seals pipe in the field. Both brands sell risers to bring the lid to grade.

Keeping the box level

A box that settles or tilts sends most of the flow down the low outlet, and that line overloads while the others sit dry. Makers sell outlet inserts to correct this. Polylok's Equalizer pushes into a 4" outlet pipe (schedule 40, SDR 35 or thin wall) and adjusts its weir in 1/16" steps, up to 7/8". Tuf-Tite makes Speed Levelers for the same job. These inserts are not on our standard stock list, so ask inside sales if the design calls for them.

Code and design

Box type, hole count, placement and distance from the tank are set by the approved septic design and the local health code, not by the box maker. Build to the design, and call us with the part list.

What to order with a distribution box

• SDR 35 solvent weld pipe and fittings, 4" solid from the tank and 4" perforated for the lines
• Effluent filter for the tank outlet, 4"x22" or 6"x22"
• Fralo by Roth or Norwesco septic tank, 1,000 to 1,500 gallon
• ARC or Cultec chambers for the leach field
• Filter fabric and detectable sewer tape

Questions about septic distribution boxes

Is a septic distribution box necessary?

A leach field with more than one line needs a way to split the flow, and a distribution box is the common one. Some sloped sites use drop boxes that fill one line after another instead. Whether a d-box is required, and which kind, is set by the approved design and local health code.

What are common septic distribution box problems?

The most common is a box that settles or tilts, so one line takes most of the effluent. An effluent filter at the tank outlet helps keep solids out of the box. Outlet leveling inserts from Polylok and Tuf-Tite correct small tilts.

How far does a distribution box have to be from the septic tank?

The distance is set by your local health code and the approved septic design, and it differs by state and town. Follow the design drawing. Yankocy supplies the box, pipe and fittings. It does not design systems.

What is the difference between a Tuf-Tite and a Polylok distribution box?

Tuf-Tite boxes are square polypropylene boxes with a fixed hole count and snap-in seals. Yankocy stocks the 4-hole 12" and 7-hole 16" square Tuf-Tite boxes. Polylok's round boxes let the installer set the inlet and outlet heights. The 20" Polylok comes in 6-, 7- or 8-hole models. Yankocy stocks both brands.

Is an NDS catch basin the same as a distribution box?

No. An NDS square catch basin collects surface water from a yard, driveway or downspout and sends it to drain pipe. A septic distribution box splits effluent evenly between leach field lines, with level outlets set below the inlet. The 18" and 24" square boxes sold for drainage are NDS catch basins, not d-boxes.

Last updated November 2, 2026

Yankocy sells septic distribution boxes wholesale to lumber, mason and landscape yards. Buying for your own home? Your local lumber or mason yard can order it for you.

Septic distribution boxes data sheets and sources

• Tuf-Tite: 4-Hole Distribution Box
• Tuf-Tite: 7-Hole Distribution Box
• Tuf-Tite: Distribution and drop boxes
• Polylok: 12" Distribution Boxes
• Polylok: 20" Distribution and Valve Box
• Polylok: Equalizer
• NDS: Square catch basins

Related to septic distribution boxes

• Septic tanks
• SDR-35 pipe
• NDS Flo-Well dry well
• NDS channel drains
• All drainage & septic