Watch how a drain field works

Follow the blue flow from the septic tank through the distribution box. The animation switches between two trench lines every six seconds so you can watch the soil wetting and draining. Both lines can receive flow at the same time in a gravity-fed system.

Swipe the diagram sideways to see all the labels.

One distribution box feeding two drainfield trenches A top view shows one inlet and two separate outlet pipes. A trench cross-section shows effluent leaving a perforated pipe, passing through gravel and soaking into the soil below. Lawn cutaway · top view Drain Field 1 Drain Field 2 From septic tank Distribution box Inside either trench Perforated pipe Gravel Soil below

The liquid leaving the tank is called effluent. It flows by gravity to the distribution box, which divides it among the trenches. Effluent leaves through small openings in each pipe, passes through gravel, and seeps into the soil. Soil particles and naturally occurring microorganisms help remove contaminants as the effluent moves through unsaturated soil. EPA septic system types