If it doesn't work, you might try hydrochloric acid. It is very cheap ($4/gal, hardware stores or pool supply stores) and will obliterate pretty much anything except metal, plastic and glass. Obviously, it is also dangerous and can give off toxic fumes, though. I have a pool, so I always have some around. It works great for random stuff like that, just be careful, do it outside and try to hold your breath when you're around a reaction. You can get it on your skin, but you have to wash it off within a minute or two or it will burn. Also it will probably blind you if it gets in your eyes.
I have seen it take the paint off a beer can in a matter of minute, that's why I thought I'd mention it. It is pretty dangerous, though, so I'd try the StarSan first.