What is a watertight receptacle designed to receive the discharge of sewage and permit settling of solids?

The correct choice is the septic tank, which is specifically designed to receive sewage discharge and facilitate the settling of solids. This component plays a crucial role in conventional septic systems. When wastewater flows into the septic tank, its design allows heavy solids to settle at the bottom, forming a sludge layer, while lighter materials like grease and oil float to the top, creating a scum layer. The tank is watertight, preventing leakage into the surrounding soil and ensuring that only partially treated effluent exits to the drain field for further treatment.

This process reduces the amount of solids and helps in the natural breakdown of organic matter through anaerobic digestion by bacteria present in the tank. By effectively managing solid waste, the septic tank is vital for maintaining the efficiency and longevity of the overall septic system.

In contrast, while a sewage basin may collect sewage, it does not provide the same level of treatment and is not designed for the settling process. A holding tank temporarily stores sewage but lacks the treatment processes present in a septic tank, which is designed for solids settlement. Lastly, a wastewater treatment plant processes larger volumes of wastewater through a complex treatment system, rather than serving the specific and localized function of a septic tank in managing household sewage.