What is the primary purpose of a septic tank?

The primary purpose of a septic tank is to remove solids from sewage through settling. In a septic system, waste from the home is directed into the septic tank, where it undergoes a natural process of separation. As wastewater enters the tank, heavier solids settle to the bottom, forming a sludge layer, while lighter materials such as grease and oils rise to the surface, creating a scum layer. The tank is designed to allow this settling process to occur, effectively separating solids from liquid waste.

This settling process is crucial because it reduces the amount of solid material that can move into the drain field, which is essential for the system's functioning and longevity. Additionally, the liquid effluent that remains in the tank, after solids have been settled, is then allowed to flow out into the drain field for further treatment through soil filtration and microbial action.

Other options suggest processes that are not the primary function of a septic tank. For example, while it does play a role in treatment, it does not chemically treat waste (the original wastewater is primarily biologically treated inside the tank and beyond in the drainage field). The expectation that it can filter all contaminated water does not align with its design, as more processing occurs outside the tank. Lastly, storing sewage waste indefinitely