At some point in the game, you've got to put a premium on your time, versus the money that might be saved by trying to save that tank. The guy's tank that you linked to was a motorcycle tank, for God's sake, so at the most he put 8-10 gallons of vinegar through it.
A Fairlane tank? What is that, 18 gallons? Times two?
Just get a new tank. There are plenty of other things to tinker with, I'd think.