(05-17-2018, 10:11 AM)American Nomad Patriot Wrote: Best way I knew to do it was to fill with about a couple pounds of sand and gravel and then fill with water while it's off the truck.
With rusty motorcycle gas tanks, steel gas cans, and old steel generator gas tanks, I remove the tank, plug the outlets, pour in a pound of random screws, nuts, and bolts. Then add a half gallon or so of CLR cleaner.
Shake vigorously for a little while, (its VERY noisy!) then let it sit, soaking, for a while in warm sunny weather, on each side, shaking in between resting periods.
This takes a day or two.
Then empty all the crap out, rinse thoroughly with soap and water. Invert, and let dry a couple of days.
Another step that I use sometimes is Kreme, gas tank sealer.
Admittedly, this is a lot of work, and the large tank on this truck would probably not be a candidate, but maybe a pressure washer using CLR and an angled nozzle would work.
Or, maybe a new aluminum fuel tank!
($$$)