The septic tank is a buried, watertight container typically made of concrete, fiberglass, or polyethylene. It holds the wastewater long enough to allow solids to settle out (forming sludge) and oil and grease to float to the surface (as scum). It also allows partial decomposition of the solid materials. Compartments and a T-shaped outlet in the septic tank prevent the sludge and scum from leaving the tank and traveling into the drainfield area. Screens are also recommended to keep solids from entering the drainfield.
Newer tanks generally have risers with lids at the ground surface to allow easy location, inspection, and pumping of the tank.
Newer tanks generally have risers with lids at the ground surface to allow easy location, inspection, and pumping of the tank.