A septic system is a sewage treatment and disposal system buried in the ground. It is composed of a septic tank and a leach field or trench. Household sewage (wastewater from sinks, toilets, showers, washing machines, garbage grinders, and dishwashers) generally flows by gravity into the septic tank. There, heavier particles settle to the bottom and scum rises to the top. Bacteria in the tank help break down some of the solids.
The sludge and scum remain in the tank, and the effluent (liquid) flows to the leach field, where it is distributed over crushed gravel or absorbent soil.
As the sludge level increases, more solids escape into the absorption area. If too much sludge accumulates, no settling occurs before the sewage flows to the soil absorption area. To prevent this, the solids in the tank must be pumped periodically. Septic tanks will not fall immediately if they are not pumped. However, an un-maintained septic tank is no longer protecting the soil absorption field from solids. Continued neglect may result in system failure and even replacement of the soil absorption field.