:shock: Dejavu all over again... I did this same project a few months ago... My problem was that when you hook up the outlet hose and run it down through your scupper hole, it's going to create a siphon keeping the water level at whatever level your hole is, but it's loud and anoying (this happened when I tested it in my tub)... Hope you have a screen for the intake hose cuz your gonna get eel grass fouling up your pump otherwise... also, you may or may not notice this but 5 gallons of water is a lot to have above your center of gravity, so be careful when in rough swell... About priming, I carried a gatorade bottle with me and poured it down the exhaust end of the pump. You have to turn the pump facing directly upwards to allow the air to escape, then turn it back and forth to allow any trapped air out as well..pain in the ass I know, so a priming bulb is better... OH, and the water pressure in your tub is different than the water pressure in the ocean....where does this cause a problem... When you have the exhaust hose in submerged beneath your kayak through your scupper hole, the water doesn't flow freely out of your tank, causing overflow in your tank..... that may solve a siphon problem though :? ... anyway, after wasting close to $150 bucks on tools and required parts, (wood bits, drill bits, buckets, check valve, pump, wire connectors, glues, epoxies, hoses, pvc fittings, brass fittings, screen, hose clamps) I gave up and saved for a kayatank... no problems, more practical, sits beneath the water level (no priming)...my .02 cents
hope your experience is better than mine...