[WardL]

I expect the rust came from the ethanol in the gasoline and not your recent fill with water. If you do epoxy coat the tank, be sure it will handle ethanol. Many older boats have epoxy lined tanks not compatable with ethanol. I would choose something that will handle up to 85% ethanol. I'm not saying you should use a new coating of some kind, but it seems like you want to do something to stop the rusting.