Which component of a septic system primarily holds and treats the wastewater?

The septic tank is the primary component of a septic system designed to hold and treat wastewater. Inside the septic tank, the wastewater is separated into three layers: solids (sludge) at the bottom, liquid effluent in the middle, and scum (grease and oils) on top. The tank provides a space where the anaerobic bacteria can break down the organic matter in the wastewater, leading to partial treatment. This breakdown process reduces the volume of solids, making it easier for the subsequent system components, like the drain field, to handle the treated effluent.

The drain field, while important for further treating and dispersing the treated effluent into the soil, does not hold wastewater itself. Instead, it functions as the final step where the effluent is filtered through the soil, allowing for additional treatment before entering the groundwater. The distribution box is a component that directs effluent from the septic tank to various trenches in the drain field but does not treat or hold wastewater. Finally, the pumping station is used to facilitate the movement of wastewater to different areas of the system but is not involved in the treatment process.