Most septic systems are a simple design with a two compartment tank and drain field. The septic tank is a watertight box, usually made of concrete or fiberglass, with an inlet and outlet pipe. The septic tank treats the wastewater by holding it in the tank long enough for solids and liquids to separate.
Sludge and Scum
Solids lighter than water (such as fats, oils, and grease) float to the top forming a layer of scum. Solids heavier than water settle at the bottom of the tank forming a layer of sludge. The layers of sludge and scum remain in the septic tank where bacteria found naturally in the wastewater work to break the solids down. The sludge and scum that cannot be broken down are retained in the tank until it is pumped.
Standard Drain Field
A standard drain field is a series of trenches or a bed lined with gravel or course sand and buried one to three feet below the ground surface. Perforated pipes or drain tiles run through the trenches to distribute the wastewater. The drain field treats the wastewater by allowing it to slowly trickle from the pipes out into the gravel and down through the soil.