Septic tank
While a properly maintained and located septic tank does not pose any more environmental problems than centralized municipal sewage treatment, certain problems can arise with septic tanks in unsuitable locations. Since septic systems require large drainfields, they are not suitable for densely built areas.
Flush toilet
A toilet need not be connected to a water supply, but may be pour-flushed. This type of flush toilet has no cistern or permanent water supply, but is flushed by pouring in a few litres of water from a container. The flushing can use as little as 2–3 litres. This type of toilet is common in many Asian countries. The toilet can be connected to one or two pits, in which case it is called a "pour flush pit latrine" or a "twin pit pour flush pit latrine". It can also be connected to a septic tank.