My house has well water and with that a high mineral content, AKA hard water.
Toilets are a bitch to keep clean and I had to resort to caustic solutions like Santeen (acid) which is bad for septic fields.
I saw a blurb on a website about the wonders of WD-40, one of its many wonders is to spray the toilet bowl liberally.
Holy shit! It really does work? Waste slides away and mineral buildup is gone.
And WTF is in those Mr Clean Erasers? Those fuckers work great.