Re: Bilge pump non return valve.
I wouldn't use a check valve on an automatic centrifugal pump where's there's not problem to solve. A problem would be that you have such a long discharge hose that when the pump stops the hose water drains back causing the pump to cycle again. The risk you have with an automatic pump is if the valve sticks when you're gone your pump is OOC until you get there and fix it. Over time that may burn out the pump.
I do use a large bronze foot valve on my large manual diaphragm pump which reaches down into a bilge pocket that's about 2 feet below the waterline. This has a large hose and I'm pumping a lot of air to get to the water. The biggest risk is of it being stuck closed in an emergency so I have to flush it periodically. I can pull the hose and bang on it if it's stuck.