Welding in a bung on a steel fuel tank.

I would have silver brazed instead of welding, "less heat," but that's fine. I don't like to drill something like that. Instead (this fitting may be too big to do this) I like to start a small hole, and then using awl and tapered punch, work it out larger. Heat it some to soften. When you are done, you have a nice fat ridge that reinforces the surrounding tank, makes it easier to weld without buring a hole, etc. More material. I have NEVER had a problem welding a tank. Flood it with CO2 after you get "so much" water in there.