Waste material from the house enter the septic tank slowly so that solids and greases can either settle to the bottom and form a sludge layer or raise to the top and form a scum layer. In between the sludge and scum layers is a layer of liquid waste known as effluent.
When waste enters the tank, bacteria begin to break down the solid materials. This process is called decomposition. As a result of decomposition, solids are reduced, leaving a residue behind in the tank. As time passes, the remaining residue builds up and must be removed via pumping to prevent it from entering the tile field and clogging the system.
The center liquid layer flows slowly from the tank into the tile field. Pipes in the tile field are perforated. This allows the liquid to be distributed equally in specially prepared gravel filled trenches. Once the liquid reaches the trenches, it soaks into the soil. The soil then acts as the final filter in the treatment of waste received by the septic system.