Fuel tank coating inside and out??

Many years ago a good friend bought a used motor cycle that had a thick coating of some product on the inside of its gas tank. About 2 months later the bike fell ( or was dropped ) and there was a tiny dent made in the tank. The lining crap shattered into chunks that would not come out through the fill hole. That was all I ever needed to see.
Another tank would be my only route.