How to clean rust out of a fuel tank

[radare]

I've restored four rusty fuel tanks, to date, and have honed a process which works quite well:

• 1. Drain tank and make sure all traces of gas are out of it.
  2. Seal the petcock hole so the tank will hold liquid.
  3. Go to Wal Mart and buy a gallon of Castrol's Super Clean degreaser. Pour that in and let it sit for about an hour. This will clean out any gunked fuel and will allow the acid to dissolve the rust.
  4. Go to Home Depot and buy a gallon of Phosphoric Acid. It's green and sells as metal Etch and Prep. You'll find it in their paint department. The phosphoric acid will remove any remaining fuel varnish and will also remove the rust inside the tank.
  5. Pour half of the gallon of Etch and Prep in the tank and seal the filler hole.
  6. Shake the acid around and let it sit. Rotate the tank slowly over the next hour, letting the acid sit on different parts of the tank. You want to do this until you get all the rust out of all of the tank sections.
  7. Dump out the acid and fill then tank with about a gallon of hot water.
  8. Shake the tank thoroughly to remove the acid/neutralize it.
  9. Pour out the water and pour in a 1/2 gallon or so of Denatured Alcohol. The alcohol will absorb the water and prevent flash rust. Denatured alcohol is very vapor potent so do this where you have plenty of fresh air and are away from any flame sources (pilot lights, etc).
  10. Shake the alcohol around thoroughly and pour it out.
  11. Immediately spray a can of WD-40 into the tank. Open up the petcock hole so the WD-40 can drain out as you do this. The WD-40 will carry out any remaining water/alcohol and will prevent the tank from rusting.
  12. Finally, pour in about a 1/4 gallon of gasoline and shake around on the inside of the tank to remove the WD-40.

Some notes: The denatured alcohol will disolve your paint. Be careful with it. The phosphoric acid will damage your skin. Wear gloves.