The ingenius way to clean out a semi-rusty gas tank:
1st, we used garden rocks from walmart and tossed in a few handfuls in the tank, we used a teeter-totter motion (My dad and I holding the tank at each end, one going up, one going down). This was like a rock tumbler, knocking off TONS of the rust.
Step 2, take out the rocks, nothing really fancy... Putting fingers inside the sending unit hole and catchign rocks as they roll past.
Step 3, while vacuuming took a good bit of the powdered rust out, it couldn't get it all. Thus, our ghetto... HIGHTECH FILTRATION DEVICE:
Fuel fitting form the sending unit, to rubber line, through a jeep filter, through the screw-on filter, down to the electric fuel pump that was on the truck when I bought it,and back into the gas tank. Run it for a few minutes, shake the truck (easy when your shocks don't stop the sway), and let it filter out the shacken up rust. After 15 minutes, the gas was coming out of our little rig clear as pump-fresh gas.
:metal:
Started it up on it's own tank in nearly a year. Just gotta have time to let it warm up and get the idle set and she'll run like a beast again.