[swedishsteel]

I have a D6 caterpillar that plugged the fuel line up--discovered the tank had a LOT of varnish and gunk in it. Did some research and learned that lye works good as a cleaning agent, so I put about 10 lbs of lye in the 75 gallon tank and filled it with water. Then I washed some small pea rock and put a couple gallons of that in. Strapped it to my tractor wheel/tire and rotated it by hand a couple times a day. It got real clean, but still had some rust from condensation over the years, so i filled it up with a solution of molasses and repeated the process. Just monkeyed with it when I thought about it so this was over a month or so, but the tank came out really clean. Did cut a 4 inch round access hole in the top because there are baffles inside, and made a 1/4 inch aluminum plate cover for it that can be used in the future. Once the molasses solution is drained out, put some fuel or WD40 in and slosh it around, or surface rust will start on the newly bare metal. It was a whole lot less labor than wire wheel etc, and with that size of tank it would have been impossible.