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.
Autonomous building
Electric incinerating toilets turn excrement into a small amount of ash. They are cool to the touch, have no water and no pipes, and require an air vent in a wall. They are used in remote areas where use of septic tanks is limited, usually to reduce nutrient loads in lakes.