A septic tank is an underground container usually made of concrete, fiberglass, or heavy plastic into which wastewater or sewage flows for the initial sewage treatment. Septic tanks are most commonly used in rural areas that are not connected to a public sewerage system. The treated liquid effluent is generally disposed of in a septic drain field which allows for further treatment.
Since the rate of accumulation of septic sludge is almost always faster than the rate of decomposition, the accumulated sludge must be removed from time to time. This is done with a vacuum truck.
Great care must be taken to make certain that a septic system cannot contaminate aquifers that provide a source of drinking water.