Is there any chemical or anything that you can swish around in the gas tank to remove rust in there? or is the tank just doomed for the remainder of its life?

 

If you chemical a tank, you will have to reline it before use as the chemical of choice (muratic acid) opens the pores in the metal which induces "flash" rust After you are done cleaning your tank, Use Redkote, Creme, or POR-15 to reline your tank should cost you 30 to 45 bucks for the whole procedure, or take it to a rad shop and get them to do it.