Like Gun Doc said, also, just for future info, a Friend of mine used to clean rust out of the old metal boat motor gas tanks, by putting a little oil in it, and putting about half a pound of bird shot, or sometimes steel bb's , and then putting on a vibrator for a while. When he was done, it looked like a brand new tank! Could put some bird shot in, and put it on a vibrator, and let it beat the snot out of the rust. Phosphoric acid will take rust off instantly, but be sure to rinse well with a solution of baking soda, and water. Try Gun Doc's suggestion. Good luck.
Wayne