A septic tank is a chamber made of concrete, fiberglass, PVC or plastic, used as the primary treatment of wastewater and sewage. Settling and anaerobic processes reduce solids and organics, but the treatment is only moderate.  Septic tank systems are a type of onsite sewage facility (OSSF). They are used in areas that are not connected to a public sewage system. The treated liquid effluent then drained into a leaching field which provides further treatment. However, groundwater pollution may occur if the system is not functioning properly.

The term “septic” refers to the anaerobic bacterial environment that develops in the tank which decomposes the waste discharged into the tank. Septic tanks can be coupled with other onsite wastewater treatment units such as biofilters or aerobic systems involving artificially forced aeration.

The rate of accumulation of sludge is faster than the rate of decomposition. Therefore, the accumulated fecal sludge must be periodically removed which is commonly done with a vacuum truck.