Bacteria in the system help to break down organic matter in the wastewater. This process requires time. To permit enough time for settling and flotation, regulations require that septic tanks be sized according to the expected daily flow of wastewater from your home. Septic tanks can be constructed of concrete, fiberglass or polyethylene, and must be large enough to hold one day's flow of waste water from your home. Solids settle to the bottom.
Light materials float on the surface and only the wastewater filters out into the drain field.
The subsurface disposal area generally consists of a distribution box and perforated distribution lines installed in subsurface gravel-filled beds or trenches. The subsurface disposal area receives wastewater from the septic tank and removes harmful, disease causing microorganisms, organic chemicals and nutrients. For this part of the system to function properly, it must be constructed carefully on suitable soil. The soil also needs time to filter out these harmful materials from the wastewater. State and local regulations that determine what constitutes suitable soil have been developed after careful consideration of many factors that affect a soil's ability to adequately treat domestic wastewater.