If you are on bore water these stains just keep happening. I find the best is to scrub with domestos.If the stains are really stubborn then use a household cleaner like ajax,jif etc. and a steal scourer.

Use Harpic septic tank toilet cleaner,your toilet will look like new,its a very popular cleaner.

the best thing i have used to clean a toilet ring is bleach and a sos pad

I think the best thing to clean a toilet bowl is get some rubber gloves and some bleach as well as some type of scrubbing pad and go at it.