What is a septic tank primarily used for?

A septic tank is primarily used as an underground chamber for treating domestic wastewater. This vital component of a septic system serves to receive and hold sewage from household plumbing. It allows solids to settle at the bottom, forming sludge, while lighter materials such as oils and greases float to the top, forming scum. The tank provides an environment where anaerobic bacteria can break down the organic matter, resulting in partially treated wastewater.

This partially treated effluent then gradually flows out of the tank into a drain field, where it is further filtered and treated by the soil before reaching groundwater. The design and function of a septic tank are specifically tailored for managing the waste produced by residential households, making it an essential part of waste management in areas not connected to centralized sewer systems.

The other options do not align with the purpose of a septic tank: hazardous waste storage is not a function of a septic system; filtration of groundwater is not directly handled by a septic tank; and an overflow tank for rainwater serves a completely different function, unrelated to the treatment of domestic wastewater.