Probably it was Permatex Gas Tank And Radiator Repair. Also very good
for radiator leaks, as I have found out in my unfortunate experience.
I can't say for certain, but I'm pretty sure this is the same epoxy
putty they sell as Permatex Weld-Stik, but I have always suspected
that you get less of it for more money for not knowing what to buy. Of
course, with as little as one needs, and as cheap as it is, it doesn't
matter much.

On 5/16/05, Jim Felder <felder@knology.net> wrote:
> For the second time in two years, I've smacked the bottom of my diesel
> tank and ended up with a leak that was stopped using the FLAPS PermaTex
> brand Gas Tank Sealer.
>
> I don't remember the exact name (and threw the package away) but you
> can't miss it... it's a roll of black compound with a white center,
> about four inches long and a half inch in diameter.
>
> To use it, you cut off a small piece and knead it till it turns a
> uniform gray and becomes soft. You stick it over the leak and flatten
> it.
>
> Both times I have sanded the spot first. the first time I used it I
> drained my tank first so no diesel fuel was leaking out. This time I
> didn't even do that as I had just filled up.
>
> It's amazing that the stuff works with greasy diesel fuel streaming out
> of the tank,  but it does.
>
> Highly recommended repair kit addition.
>
> Jim
>