Yes there are chemical treatments to fix the tank but you still have to do the dad dance.
Search for tank sealers. Some are out dated like petseal, whick breaks up in ethanol. There are others, the one I used came from tank care products (I think). Several years ago now. Still have the pot I mixed it in and nothing, NOTHING from bleach to battery acid has so much as stained it.
Handfull of gravel, some white spirit and a dad dance does start things off though.......