That "rust" is more likely Iron Bacteria and is very pervasive. We have learned to live with underwear (Bleach not kind to a Septic tank) that is no longer white and stains in the dishwasher. We occasionally use Rust-Out but is tedious to use and expensive.

For the toilet we got a thing called "Kaboom" dumbest name ever. It uses large white Chlorine tablets and hangs in the tank ABOVE the water level so it does not affect the water in the toilet tank. I had tried some of the in-tank things and they ate the rubber seals.

Anyway, the kaboom tablets are expensive so I got some Brominator tablets for cleaning swimming pools. About 30 x 1" diameter tablets for about 8-bucks.

Honey has not had to clean the toilet bowls for two years. Awesome thing.

I have nothing to do with Kaboom or the bromine tablets, just a very happy customer.

For stains already n the bowl, use Rust-Out and make a loose-paste (pancake batter) and brush it on. It has to "work" for about 20-minutes so you need to go back every five minutes and brush some more on as it dries out and stops working. A royal pain, but once the stain is gone the tablets will keep it that way.