Just about any acid will get rid of the rust.
Vinegar is acetic acid
Muriatic is 35% hydrochloric acid
"the Works" is pretty dilute hydrochloric acid
Naval jelly is phosphoric acid.
Pick your poison any of them will do.
You'll quicken the process with some sort of abrasive (bbs are okay but just toss drywall screws in there, they are way sharper, how is a round bb going to scrape your tank? The banging action would help but scratching is better)
I just like HCl because it's quick and easy.