A septic tank with a pump is an underground tank for wastewater treatment in which waste is decomposed biologically and emptied. Waste enters the tank and separates into three layers: scum, effluent, and sludge. Scum, made of fats and oils, floats to the top, while solid waste forms sludge at the bottom.
The middle layer, called effluent, is mostly water, which flows to a drain field for soil filtration. A pump may be used to move the effluent if needed. Properly installed septic systems require minimal maintenance and can be made of concrete or fibreglass.