1980 moped question, yes... moped question!

[jwclbi]

Ok I recently aquired a 1980 "puch" moped, which i have gotten to run. Its really rather funny. The problem is it sat in south Florida and Bahamas for its entire life, so the insde of the fuel tank is rusted, and cant be removed. A friend of mine told me there is a series of chemicals that can be put in the tank to create a coating to restore it but doesnt know what its called. Anyone hear of anything like this? Let me know if you can, thanks.