I have a 94 201 Pro XL, same situation, one tank had not been used for some time and was nasty. I took the tank out (actually, not that hard at all) and tried everything I could think of to clean, steam, lye, acid; nothing cut the gunk. Finally, I went to the gas station and put in 5 gallons of E85. As the gas sloshed around on the way home, it completely cleaned the tank like new. I filtered the E85 through 4 fuel filters and then into my flex fuel Silverado to get rid of it. E85 is about the best cleaner you can find, and it will break down any old gas or gunk because it is an extremely efficient solvent. It will also remove any moisture (Ethanol attracts water, which is why it's bad for boats, but when used in this way it works to your advantage). If you don't want to take the tank out, you could pump the E85 in, drive around a bit so it can slosh, then use an auxiliary fuel pump to pump the fuel back out of the tank. I would take the tank out however, that way you aren't pulling any crud though your fuel system.