A Sump

1. A hollow or pit into which liquid drains, such as a cesspool, cesspit or sink. Sump - Wikipedia
2. The lowest part of a mineshaft into which water drains.
3. A completely flooded cave passage, sometimes passable by diving.
4. (automotive) The crankcase or oil reservoir of an internal combustion engine.
5. (nautical) The pit at the lowest point in a circulating or drainage system (FM 55-501).
6. (construction) An intentional depression around a drain or scupper that promotes drainage.