This thread has really gotten sidetracked and I'm a little dissappointed with it. I wanted to talk about a product which would be applied to rust and would stop it and convert it to a paintable surface. Like I thought I might try on the outside/underside of the tank. Rust can be seen in the photo. I have already treated to inside and it looks very nice, like it should. I am impressed with a product that offers such a solution to rust.
The problem I have is that if I remove the rust on the bottom of the tank( and many vintage tanks look like this), I may need to paintit and I won't be able to match the color, so perhaps I could use an epoxy black or something. I guess anything would work.