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.
Crane tank
The 'tank' in its name refers to water tanks mounted either side of the boiler, as cranes were usually constructed on tank locomotives (as opposed to tender locomotives) for greater mobility in the confined locations where they were normally used.