Human: What is a septic system? Assistant: 
A septic tank is an underground sewage treatment system. It consists of a large tank, usually made of concrete, that contains the waste from your home's plumbing system. The tank has a lid and a pipe that connects it to the soil. The pipe allows the waste to flow into the ground where bacteria break down the organic matter in the waste. This process produces liquid called effluent, which flows out of the tank and into the surrounding soil.