Tip I learned on welding tanks,mainly gas tanks on Harleys. Wash them out good.Fill them half full and roll the over where you are not welding. Done this half dozen times and never issue. I have welded on block and had fumes in oil blow a brand new mag. valve cover off in pieces. For a quick fix I carry a epoxy tank repair that is two part epoxy almost clay like.You mash them totehr and apply to tanl.Has always worked even when tank was dripping when applied. Can not remember name I get it at most any parts store.It is black and gray in roll about 3/4" and mayb e 2 -1/2 long. Only 8 or 10 bucks and worth a try.