Jabsco Bilge / Graywater pumps are a series of efficient single-chamber diaphragm pumps.

The models 37202 and 50880 which have 25mm connections are suitable as a bilge pump or as a gray water pump to pump away water in the shower and sink.
Model 50890, which has a 38mm connection, is a waste pump that is for emptying black water in the toilet system.