gas tank cleaning...

the oe fuel tank on the 68 barracuda has a pretty good dent on the bottom side,, I picked up a used tank from a 69 barracuda off this forum some time ago and I am getting close to installing it.

on the 69 tank, looking in through the inlet and sendor opening,, I can see some discoloration on the sides,, nothing flaky or rusty looking,,

I know I can get the outside sand blasted,, what about cleaning the inside?

One thought I had was putting a couple gallons of evaporust inside, sealing the openings then rotating the tank around for a couple of days,, any better ideas?

anyone have luck with gas tank sealers-coatings,, or should I only use that if I see flaky rust inside?

thanks