With luck any aluminum tank you buy will have been properly pressure tested at the manufacture before delivery. Aluminum is soft and thus the plugs used for pressure testing tend to be harder than the aluminum and can bugger up the threads slightly.


For safety's sake I always chase aluminum threads before installing fittings into an aluminum tank. You will need an NPT tap to match the tank tapping threads for this task. Don't go crazy all you want to do is make sure they are smooth and free oil, debris or shavings. These tappings were all 3/8 X 18 NPT. After you chase and clean the tappings you'll then want to vacuum out the inside of the tank.