My fathers pump will lose its prime if he doesn't run the pump every 3-4 hrs-flush toilet or turn on faucet. we put a new check valve by the pump(not a submersible) between it and the well (shallow well). rebuilt pump and new bladder tank. could it be foot valve at bottom of draw pipe or porous draw pipe? well is probably 50+ yrs old. Any feedback would be appreciated. Thanks Drv