The best way to learn is to
trace the hoses. In our boat, the electric bilge pump hose runs to and through the manual bilge pump, one hose. I found that out by simply following the hoses from the bilge to the transom. There is only one outlet at the stern. Some boats have either been built or modified by POs to have separate hoses for each pump. Some use one outlet with check valves (a solution I find unacceptable) or use two separate through hulls for water outlet. Go find out what you really have.