My 1994 C30 has a foot operated pump in the aft bulkhead of the galley. It is mentioned briefly in the book that came with the boat as either a galley sink drain or an optional salt water sink pump. When I step on it I can hear water sloshing but I don't know where it's input is or where it pumps to. I'm concerned because I can't figure out how to winterize it. Any ideas what it is and how it works?