A septic tank is a key component of a septic system. it is a small scale sewage treatment system in areas where there is no connection to city or local government systems. Components of a septic system are mandated and restricted by local governments and include alarms, pumps and sand filters and a clarified liquid disposal system called a septic drain field. Approximately 25% of the North American population relies on septic tanks. This can include small towns, rural areas and the suburbs.