Pretty tough to weld aluminum filled with water. Actually, welding gas tanks is pretty simple, you run an exhaust hose into the tank from a running engine, that creates an inert atmosphere. Weld away. JB Weld might work if you can get the crack clean enough and there is not much flex to the tank. JB doesn't flex well at all. If you use JB and then end up getting it welded, your weldor will not be too please with you 'cause he (or she) is going to have to grind it off. BTW, the best heliarc weldors that I knew were women.
On afterthought, if you are going to weld it yourself, don't do it indoors with CO pumping into the tank. And yes, the tank will need to be degreased, the hot water and Dawn will work. Alumimun needs to be pretty clean before being welded. I'm surprised that you can't get a new tank for some of the costs quoted, but then its been more than 20 years since I made my living welding.
[ 04-18-2003, 03:22 PM: Message edited by: James in Idaho ]