The typical septic tank is a large rectangular or cylindrical tank made of concrete, fiberglass or plastic. In New Mexico, septic tanks must have two compartments, the first being about twice the size of the second.
All the wastewater from your house is received by the septic tank. Tees or baffles are provided at the tank’s inlet and outlet pipes. The inlet tee slows the incoming waste and reduces disturbance of the settled sludge. The outlet tee keeps the scum layer in the tank.
Newer systems have an effluent filter. The filters need to be cleaned when the tank is pumped. It is important to have a garden hose available so the filter can be cleaned.
When the liquid and solid wastes enter the tank the bacteria, which live in the tank, use the organic material as food. However, they cannot use all the food that enters the tank and in addition they are producing their own waste material. As a result there is a slow accumulation of solid material (called sludge) at the bottom of the tank. There is also a buildup of greases, oils and fats that float on the surface of the septic tank contents (called scum).
The solids, which remain in the tank, must be removed by periodic pumping to prevent them from overflowing in to the absorption field. The frequency of septic tank pump out varies depending on the tank size and the amount of solids entering the tank.