[wrath]

If you want to remove rust stain and rust altogether, it's tough to beat muriatic acid (aka weak hydrochloric acid) is super cheap for the job. Need to wear gloves. It's cheap at the home improvement store known as concrete etcher. I use it for all sorts of ****, including cleaning pontoons. Just don't do it on concrete or limestone as the fumes are terrible as it reacts with it.

You can also get HCl in gel format which is what I prefer from a lot of industrial supply houses but it's expensive usually...

You can get weaker HCl at auto body refinish places but again it's usually at a premium. Sometimes they have phosphoric acid. Sometimes they sell them as gel and or foaming type, which again is super handy for vertical surfaces.

Citric acid (like what is found in Iron Out) is handy, because you can get it in gel format at any store so you can spray it on and move it around and not pay attention to it like most other bathroom cleaner sprays that have phosphoric and glycolic acid (AKA CLR) that dry fast and run. I use the Iron Out gel for bathrooms on painted surfaces a lot.

If you're super impatient like me, you can skip using the non-scratching scotchbrite pads and use 2000 grit wet/dry to speed things up with the muriatic acid.


Edit: You can also use oxalic acid because it's way less abusive on iron... but it's super poisonous and can be absorbed through the skin way easier than the rest of the acids (that usually just cause burns and whatnot). I use it on thin iron pieces I can't risk pitting on.