This is actually a steel motorcycle tank, but the question is the same regardless of if it's a motorcycle or a truck tank. I want to grind off the stock tank bung (where the fuel petcock screws on) and weld on a new tank bung. I have a MIG welder so I know I can weld it, but would it be safe? Obviously one would drain all the gas. Would I fill it with water? Or something else? I am of course concerned about gas vapors going boom. What do you guys think? I think the local radiator shop fixes gas tanks, so they might be able to do it for me if it is a bad idea for me to do it. The other option: I could cut some of the length off my stock tank bung and use a die to thread it to stock Harley-Davidson, which is 22mm. I have not been able to locate a 22mm die. Anyone know where I can locate one? Obviously they exist, but I have not been able to find one. http://www.pingelonline.com/adaptor_plates.htm Scroll down to tank bungs and these are the ones I am looking at.