A friend of mine bought a nice boat and completely restored it. The only problem is that the tank is build in the floor and he can't take it out. It is an older boat therefore it has some rust in the tank. He tried to clean it, sucked it out with vacuum etc After a while the rust mixes with gas and the engine chokes. Is there a way to fix it, restore that tank on the inside or maybe seal the rust on the inside? Thanks for the help.