The gas tank sealer might be the best solution. However if you use
phosphoric acid on zinc, the zinc gets eaten by the acid. Then if you
use that on steel or iron, you get a zinc phosphate coating on the
steel/iron. This helps to stop it from rusting again.

Dan
RWL wrote:

If I used auto body metal prep (phosphoric acid) would that kill the
rust so that it wouldn't come back, or does it just etch the metal so
that paint adheres better?



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