I've got the same problem with a Norton tank I picked up. Looks like a Kreem liner, has a tan/ biege color to it. The stuff is peeling off the walls of the tank. I think I can get most of it out with various grabbers and someone suggested Methyl Ethyl Ketone to break dowm the rest. Its available in most paint stores but beware its nasty stuff. Eats right through your paint finish and you'll want to keep way far away from ignition scources!