Usually made of concrete or plastic, these tanks are buried underground in towns that do not have a centralized sewage system. A complete septic system is in essence an individual waste water treatment system.

The way that these systems work is sewage flows from the pipe that leaves your house to the inlet of the septic system(left). It flows into either a PVC T or an inlet baffle integrated into the tank. The purpose of this is to block scum that is floating on the top of the tank from going back into your inlet pipe and causing a blockage. The sewage flows down into the tank, and slowly makes its way to the outlet side of the septic tank. These tanks are operated full, so with every gallon of waste that goes into the tank, a gallon of waste leaves the tank, and makes its way into the drainfield. Toilet paper, grease and oils floats to the top of the tank, while food solids and other debris falls to the bottom sludge layer. The wastewater, now free of debris, makes its way to the outlet T. Many times, a filter is in place as an insurance policy just in case solids make their way to the outlet. The filter needs to be cleaned regularly in order to function properly.

Some systems are gravity-fed, which means that wastewater from the septic tank drains down to the drainfield by gravity. Some systems have drainfields that are higher than the septic tank, due to high ground water or property topography issues. The systems have an additional tank between the septic tank and the drainfield called pump chambers, which hold a sewage pump with a series of sensors that controls the pump.

The frequency of pumping depends on many factors, however most health departments recommend it be pumped every 3-5 years.