Naturally occurring bacteria act to digest the solids. The tank liquid level will fill to the outlet, which is on the opposite side of the tank from the inlet. As a given volume of wastewater enters the tank, an equal volume exits through the outlet. This liquid, known as effluent, is then routed into either a soil absorption drain field or evapotranspiration fields. Soil absorption drain fields use primarily absorption for effluent disposal.
Some disposal is accomplished by evaporation and plan uptake.
Evapotranspiration fields, on the other hand, are lined completely along the walls and bottom with watertight liners and use only evaporation and plan uptake for disposal. A septic tank system should not be treated as if it were a city sewer, where large amounts of water are allowed to go down the drain. Water conservation helps prevent overloading in the drain field. Such overloading could shorten the septic tank's life and require expensive repairs. Leaky faucets and running commodes should be repaired.