There should be a filter before the pump, is that clean?? It should self prime if you have something in the tank to pump. A Google search to west Marine says it self primes up to 6 ft. Maybe there is dirt in the check valves or diaphragm. Maybe you have a line blockage? You do not want easy priming tricks you want to determine why it does not self prime.
Put some water in the tanks above the level of the pump, disconnect the inlet line at the pump and see if water runs from each tank one at a time. If so and the pump will not pump, then you need to likely clean the pump head.
Good Luck and do not forget to tell us what you find.
Ken GeigerNorthern Dream #765