Try vintage tanks with 1/2" NGT threads
Yep those a pain in the neck, I use 1/4 SS 1/8 thick punch outs as media,
Does a very good job, but going into the tank a pain in the butt on 1/2 npt.
Phosphoric acid is the way to go to remove rust, just don't use to high a concentration or it will turn the steel black.
What do you mix it at?