The Septic Distribution Box

The septic distribution box is part of the conventional drain field system. It distributes the effluent (wastewater) evenly to the drain field (leach field).

The most common way to make this work is through the use of gravity.

Since water flows downhill, placing the box so that the water will flow into it from the tank and then on into the drain field requires only this common-sense knowledge (and perhaps the ability to shoot grades with a surveyor’s stick).

As effluent flows out of the tank, it travels a short distance into the septic distribution box. The box, which comes in many shapes and sizes, handles the effluent by sending the wastewater into various drainfield lines or trenches.

A distribution box is a concrete or plastic structure that has a number of openings. Septic pipes fit into the openings, usually with the help of a gasket. The distribution box has a cover because it will be buried under ground. For this reason, concrete distribution boxes tend to work better than other kinds, because the construction is sturdier. Also, a
concrete distribution box is easier to find (a probe rod can locate it) and inspect.

The distribution box openings can be fitted with flow leveling devices that rotate so that some openings are higher or lower than others. This is to ensure that all of the drain field lines are receiving the same amount of effluent waste.

It is important for the distribution box to work properly. An improperly working septic distribution box is a main reason for drainfield failure. The equal distribution of the wastewater will maximize the life of the drain field and the entire septic system.

An alternate distribution method uses pipes instead of a box to send wastewater into the drain field. In using this method, watertight pipes lead to the trenches in the drainfield.

There are two type of septic distribution systems, the parallel system, in which the septic distribution box sends wastewater to all the trenches at the same time, and the serial system.

The serial system sends wastewater to the first trench, then the second, and so on. This type of system has an immediate disadvantage in that it often overworks the first trench. Generally speaking, the effluent runs into the first trench until it fills up. Then it flows into the next trench, so that the first drain field line tends to be full all of the time.

Each drain field line functions separately from the other, and theoretically, if one line works less well than another, it will receive less effluent. On the other hand, a trench that drains well will receive a great deal of effluent. The efficiency of a drainfield trench depends upon the soil around it, how much sunlight it receives and other natural factors.

If a serial system fails, another trench can be added at the end, if a landowner has room to enlarge the drain field.

Time is the main culprit in a failing distribution box. The boxes are level when installed, but weather, including flooding and freezing temperatures, can make the boxes tilt to one side. Because the box is no longer even, the effluent no longer flows properly into the trenches.

The distribution box is a most important component of a septic system. Without even distribution of effluent, the drain field will be used unevenly. As trenches in the drainfield become overloaded, portions of the drain field will fail. The result of a poorly functioning septic distribution box is untreated wastewater appearing on the surface of the soil in the drainfield.


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