A septic tank is a buried, watertight container typically made of concrete, fiberglass or plastic. 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).

The septic tank also allows partial breakdown of the solid materials. Some solids are removed from the wastewater, some are digested, and some are stored in the tank. Up to 50% of the solids retained in the tank decompose, while the remainder accumulate as sludge at the bottom of the tank and must be removed.

Compartments and a T-shaped outlet in the septic tank prevent the sludge and scum from leaving the tank and traveling to the drain field.

Newer septic tanks have risers with lids at the ground surface to allow easy inspection and pumping of the tank.

The septic tank should retain the wastewater for at least 24 hours.

Septic Tank Diagram