What is a distribution box?
A distribution box is also known as a d-box.
It splits the liquid flow from the septic tank into two or more leachfield lines.
D-boxes are notoriously finicky.
When a d-box is out of level by as little as a 1/16 of
an inch, liquid tends to
flow down one line of the drainfield over the others.
Overtime this causes premature failure of the
A shovel full of dirt can easily thrown a d-box out of
D-boxes are a known problem in the industry.
The standard solution is to use levelers (a.k.a. speed
But these are not a magic bullet. Levelers just help
Besides a shovel full of dirt, what really causes a
d-box to be out of level is a
little frost heave.
Over a few years time they will shift ¼ or even ½ inch
out of level.
Go ahead and get in the habit of adjusting your d-box
every year in the
The best way to prevent frost heave is to do what they
do under railroad
tracks, place the d-box on a nice thick (1.5' at
least) bed of gravel that goes
below the frost depth.
What is the frost depth? It varies throughout the
In the mountains it is about 1' so you do 1.5' of
gravel unless you are above
4000 feet then go ahead and do 2' of gravel. On the coast it is probably 6” so
go ahead and do 1'.
Use clean washed gravel compacted in 3 or 6” lifts.
Use the more expensive levelers—they work better.
Ideally, use a tipping-style distribution box--I
manufacture these or a flout--I
My Tipping Distribution Box Story>