How big is the average septic tank?
Septic tank
A septic tank consists of one or more concrete or plastic tanks of between 4000 and 7500 liters (1,000 and 2,000 gallons); one end is connected to an inlet wastewater pipe and the other to a septic drain field. Generally these pipe connections are made with a T pipe, allowing liquid to enter and exit without disturbing any crust on the surface. Today, the design of the tank usually incorporates two chambers, each equipped with a manhole cover, and separated by a dividing wall with openings located about midway between the floor and roof of the tank.
Pit latrine
In a pour-flush pit latrine, a squatting or pedestal toilet with a water seal (U-trap or siphon) is used over one or two offset pits. Therefore, these types of toilets do require water for flushing but otherwise have many of the same characteristics as simple pit latrines. About one to three liters of water is used per flush in that case, and they often have two pits that are used one after the other ("twin pit pour flush pit latrine"). For this reason they are subsumed under the term "pit latrine". The fecal sludge that is removed from the full pits of twin-pit pour-flush pit latrines is somewhat safer to handle and reuse than the fecal sludge from single pit pour-flush latrines. However, significant health risks for the workers who are emptying the pits remain in either case.
An alternative to U-trap or siphon designs is to incorporate a counter-weighted trap door mechanism that provides an air-tight water seal in the closed position. Addition of a small amount of water (generally less than 500 ml) overcomes the counterweight and allows the fecal matter to enter the pit. The devices are sold under the name of "SaTo pan" for as little as US$1.85, and more than 800,000 of them have been installed worldwide since introduction in 2013.