Easiest way is toset the tank up so it's very stable and fill it with water to just below your cut line. Cut it with a sawzall or something that doesn't make sparks. Remember that water and electricity don't play well together. Once you have cut the top or bottom off either salvage the top or bottom...

I watched Jody's vid on this but when he is on AC brazing with Aluminium Bronze he didn't state which tungsten he was using, Zirconiated or Thoriated? I assume it would be Zirconiated so it doesn't melt but assumption is mother of all fuck ups!! Cheers for the help!