I've been restoring a historic home, which contains original historic fixtures in fabulous like-new condition, with one exception. The bathroom sink, original to the house (so I didn't want to replace it, I wanted to restore it), had a rust stain beneath the left knob.
I asked around for tips on how to fix it and was told by industry professionals everything from "use xyz harsh abrasive" (which I knew would damage the porcelain) to "it can't be fixed". Well, I didn't like any of those answers so I found this recipe, didn't think it would work, but gave it a shot anyway, and what do you know? The sink looks brand new!
How to Remove Rust from Porcelain
What is your favorite household tip?