Miguel,
Thanks for all that. Wow, you've really put a lot of 'flat' into the tube. Works better, huh? Interesting and worth a try. As for 'water testing', to late for me perhaps. I didn't catch the warnings of using water verses kerosene or smoke oil prior to testing. Perhaps running the oil through it now will minimize any further abrasion the water might cause on the pump. As far as the constant siphoning goes, don't know how best to fix that one. Perhaps a loop up higher than the tank/pump, for sure. Using a 'K&S' fuel line pinch will help during transport, etc. Not able to immediately stop the flow once the tank is filled and the pump is made ready for flight appears to be the biggest headache right now. Perhaps the thicker smoke oil combined with the little check valve in place will be enough. Unfortunately, the engine in the KingCat sits lower than the rest of the entire fuselage belly. My perfect fitting tank, BTW, ended up being a plastic liquor flask (20 oz) that fits above the hopper and between the two Kevlar main tanks - right on the CG ($5). It's fairly thick plastic too (a bonus).
You know what might work great is a JetCat type fuel valve, hooked into or mixed with the Fuel Pump command. That's positive shut off!
LKL