The septic tank is a watertight box made of precast concrete, reinforced fiberglass, or plastic placed between the house and a disposal field. The tank protects the disposal field by removing solids and grease form the sewage before it reaches the disposal bed.
When household waste enters the tank several things occur.
- Lighter solids and materials float to the surface of the tank to form a layer called scum.
- Heavier solids and the by-products of biological digestion settle to the bottom of the tank to form a layer called sludge.
- Liquid from the clear space passes out to the disposal field to be treated by the soil. If solids are able to pass through the septic tank to the disposal field the pores in the soil will become clogged, causing a bed failure.