Gas tanks are typically made of terne plated steel, which is basically lead coating.
If you don't have any rust, a good strong solvent will remove the varnish. Something like lacquer thinner or acetone. Be careful about vapors, etc. The stuff is probably more flammable than gasoline.


Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.