[greasemonkey]

I've gone through this recently with a motorcycle gas tank that had sat over winter with water in the tank. I tried oxalic acid and wasn't impressed. I ended up using Ospho (phosphoric acid) and water solution and let it soak a few days. I threw some old bolts and nuts in it, shook it violently, rinsed it and it looked brand new inside. Bike guys swear by Red Kote, so I used that for the liner. It is inexpensive and it is ridiculously easy to use. This is going to be my go-to procedure from now on. Cheaper than buying a new tank as long as you are willing to put in a little work.