[Polock Joe]

there's this too:
http://www.caswellplating.com/aids/epoxygas.htm

-works on rusted tanks well

I used this stuff on a painted sporty tank because the bottom started to seperate from the sides and would literally spray gas out the bottom. I coated it once and didn't work so then I dumped a bunch into the corner that was seperating and cured the problem. Haven't had any leaks since but now I have a half inch of sealer in the corner of my tank.....