jdl, theres probably about 10,000 posts on gas tank cleaning and sealers.
I wouldnt use gas to clean it, the fumes could ignite. If anything use diesel. Get some nice clean peagravel or a bucket of old bolts and add a few gallons of water. Plug the holes and roll it around the yard until your arms hurt. Then empty the rocks or bolts out and just stick a hose in the filler neck and leave it on for awhile, eventually all the loose rust and dirt will drain out of the bottom.
Good luck!
Jeff
