I think I agree w/Archion because I know what didn't clean a tank - a chain, 2 gallons of fresh gas, lots of sloshing, rinse and repeat 4 times.
You would think that would get rid of the sediment, but it didn't. So, I have to run two fuel filters, one ahead of the pump which catches LOTS of sediment, and one in the normal place between the pump and the carb. And, don't use the thin metal filters like were originally on the trucks as they have very coarse screen in them and are effective on flies, not gnats. One of those let enough silt through that my accelerator discharge nozzles plugged up. I use the see-thru plastic filters with pleated elements and haven't had any more problems, although I do have to change out the first filter every few months.
Check the condition of the tank on top were it lays against the frame, and underneath the plastic protector. They like to rust out there. And also get prices to steam the tank out. Then compare the price to a new tank, which I believe is only around $100.
If its just rotten gas and not much rust, few gals of acetone should get rid of the varnished gas. I did that to my 93 Explorer buggy which has the plastic tank. Someone else told me diesel fuel also cleans up varnised gas too.