Re: Priming you water pressure pump
Most likely, you either have an air leak above tank level or your pump isn't sealing completely and is allowing the water to drain back when it is off. If you have a ball valve at the outlet of the tank, try closing it when you leave the boat and see what happens. If there is still water there, then your pump is leaking back and if there is less water, then you have an air leak most likely.
Some people actually like to put their pumps really low so that gravity keeps them primed. Also, some people will put a check valve in line with the pump.
Try to isolate where the leak is (pump, connection, line, etc). Usually this means either pressure testing or a lot of patience and closing different things when you leave the boat.