What is a septic tank's function in an OSSF?

The correct choice highlights the primary function of a septic tank within an On-Site Sewage Facility (OSSF). A septic tank is designed to receive and treat wastewater from a property. Its main role is to settle solids found in wastewater and promote anaerobic digestion.

In the septic tank, heavier solids sink to the bottom, forming a sludge layer, while lighter materials, such as grease and fats, rise to the top, creating a scum layer. Between these layers, there is relatively clearer water. The anaerobic bacteria present in the tank help break down the solid material in the sludge layer, which further contributes to the treatment process. This fermentation and digestion of solids reduce the volume of waste, preparing the effluent for subsequent treatment and dispersal in the drain field or leach field.

The other functions listed in the options describe operations that occur at different stages in the wastewater management process or do not accurately convey the septic tank’s purpose. For example, pumping water and dispersing treated water play roles outside the tank’s processing function, and while filtration may occur in the drainage field, it is not a role of the septic tank itself.