However, one tell tale would be the position of the discharge piping outlet valve, it would have to be open to pump bilge water overboard. Normally it would be in the closed position.
Alternately, if this pump served a dual purpose pump capable of pumping ballast water between tanks, then valve lineup would also provide the clue. As an example, on modern US Navy ships, the condenser cooling water pump could be cross connected to the bilge in an emergency for high capacity pumping overboard in case of a major flooding incident.
George Martin