The septic tank is a small, on-site sewage treatment and disposal system buried in the ground. The modern septic tank is a water-tight box usually made of pre-cast concrete, concrete blocks, metal, or fiberglass. When household waste material enters this box, several things occur:
Solid material overflowing into the soil absorption area should be avoided at all costs. It is this solids overflow that clogs soil pores and causes septic systems to fail. Two main factors cause solid material to build up enough to overflow: bacterial deficiency and lack of sludge removal.
Bacteria must be present to digest and liquify the scum. If not digested, the scum will accumulate until it overflows, clogging the soil absorption area.
The sludge in the septic tank - inorganic and inert material and by products of bacterial digestion - is not biodegradable and will not decompose. If not removed, sludge will accumulate until it overflows, clogging your leachfield.
You are responsible for the operation and maintenance of your septic tank. The EPA recommends pumping your tank every 3 to 5 years, depending on how many people live there and the size of the system.