Gas leek?

I got my 1990 Camry back from the shop about a month ago, and the
mechanic said that there was a gas leak coming from the gas tank, he
said it was wither a breather hose or something like that. I took a
look at it and I do see some sort of liquid coming from the tank. I was
wondering how I could fix this, or would I have to get a new tank. I
was thinking of using something like JB weld, but I wouldn't know how
to get the compound to create a water proof , could somebody explain to
me how to make a good seal using JB weld or some other compound?