A marine toilet is designed to maintain sanitation on the open sea. The reasons a normal toilet will not work should be reasonably apparent. A bowl that always has water would be subject to spilling out over the sides in rough weather. As such, a marine toilet bowl is typically kept dry. Water is then pumped into the bowl before use.
A marine toilet pump can be either electrical or hand-powered, but both achieve the same function. The pump has four different lines, or pipes, representing two different systems, the "wet" and the "dry." These two different systems are manually switched between on the pump's exterior.
The "wet" system is used to pump water into the tank. Water is sucked into the boat through a valve on the boat's underside, known as a seacock. This water fills the bowl in preparation for the toilet's use. After being used, continued pumping on the "wet" setting will circulate the water, eliminating the waste. Each downstroke sucks in clean water from the outside, while each upstroke forces waste through a one-way "joker" valve.
Once the toilet has been used and water has been circulated until the bowl is clean, the user activates "dry" pumping. "Dry" pumping once again empties the bowl of all water so that it won't spill over while in transit.
Once waste water passes through the "joker" valve, waste is typically either evacuated from the boat or pumped into a storage tank. The former option often includes one further component: an electric blade that chops up waste before it is released into the water.