What is the primary function of a septic tank?

The primary function of a septic tank is to treat sewage from a building sewer. This treatment process is essential for managing wastewater generated by households or businesses that are not connected to a municipal sewer system.

When sewage enters the septic tank, it is separated into layers: solids settle at the bottom, forming sludge, while lighter materials like grease and oil float to the top, creating scum. The tank provides an environment where anaerobic bacteria can break down and partially treat the solids. This process reduces the organic material and makes the effluent safer for dispersal into the surrounding soil through the drain field, where further treatment occurs by natural filtration and microbial action.

While the tank does act as a temporary storage unit for the collected waste, its crucial role is not merely to store waste but to initiate the treatment process, preparing the wastewater for safe disposal into the environment. This differentiates it from other functions, such as discharging sewage to a municipal system or filtering rainwater, which are not within the scope of a septic system's purpose.