Re: Bilge pump non return valve.
As Maine Sail says, it's a mistake to install a check valve in line with a centrifugal bilge pump (e.g., Rule pumps). The pump can move a lot of water but doesn't have much power. Think of it as high voltage, low amperage. Use a Vented Loop instead.
The PO of our boat installed a check valve and the bilge pump never really worked. I fussed with it for the first few months of ownership until the bilge filled and the battery drained when the pump ran in a vain attempt to move the water. I installed a vented loop and haven't thought of it in 7 years.
Sabre 38 "Victoria"