Getting rust out of a gas tank
If you want to get most, if not all, of the rust out of a gas tank, before treating it:
1) Pull the tank off the bike, and pour as much of the fuel as you can get out of it into a safe container, thru the filler cap.
2) Close the cap, turn the tank on its side, remove the petcock, and drain the rest of the fuel out.
3) Flush the tank with a water hose thru the filler opening, letting the water drain out the petcock hole, then dump a quart of rubbing alcohol in the tank, slosh it around real good, and drain it. Remove the cap assembly and the sending unit, and let the tank dry out for a while.
4) Duct tape two of the openings in the tank closed, pour in a tube of 500 BBs, and tape the last hole up. Wrap the tank in an old comforter, tie it on with string or more duct tape, and stick it in the dryer. Stuff towels around the comforter wrapped tank 'til it's not quite immobilized.
5) Set the dryer for air dry, or fluff, or whatever--NO HEAT-- and let it run for 20 minutes to an hour or so.
6) Pull the tank out, unwrap it, dump the BBs out while shaking and slapping the tank to dislodge any that may have jammed themselves in a crevice. Might have to stick the narrow end of a vacuum cleaner nozzle in to get the last holdouts, but if any do get left in, the filter on the petcock will keep them out of the fuel lines and petcock.
7) Reassemble ---------------
a) The alcohol helps dry out the last of the water left after draining that. The water flushes as much of the fuel out as possible.
b) The comforter and towels keep the tank from banging up the inside of the dryer.
c) The BBs act sort of like a bead blaster. They're hard enough to clean the rust off the tank walls, but soft enough they won't put little hail-dings in it. Preach did his a while back, before having the mount on one side welded back on. My brother tried it after I told him what Preach did, and said it did wonders on the tank on his GS850 project. Jim J.D. Channelview, TX