How to fix toilet bowl stains - Saniflo SaniPlus-Round SaniPlus Macerator Toilet with Round Bowl

bleach. Leave it overnight

I just posted an answer here, but don't see it. ??

might be just stained
get a good stain remover or drain cleaner and leave it sit for a while then flush
talk with a plumber as to possible solutions

http://www.askthebuilder.com/toilet-bowl-cleaner/

What type of surface is stained?
What type of product stained the surface?

You would have to determine what the stain is before an accurate answer on how to deal with it. Can you add a picture?

Try using one of these A product called Kaboom Bowel Blaster and let it sit in the bowl for a while, then brush clean. This worked for me when others failed. You can try muriatic acid as a toilet bowl cleaner.Again let it sit for a while then brush and flush available from places like Home depot.Sometimes the toilets are not glazed as well as they should be you might call it a defect I call it poor quality control.

Probably a mineral buildup. Pour a bucket of water into the bowl so that the bowl flushes but does not refill with water. In other words you want as little water in the bowl as possible so it wont dilute the cleaner. Use an acid cleaner like lime away in the bowl. Let it set for several hours or over night,. then scrub with toilet brush. Lime away is fairly safe but try not to splash it on your clothes or yourself. Wash it away if you do.
You may have to repeat to finish the job.

Toto toilets usually have a very good porcelain finish. I would first try a toilet bowl cleaner or a rust remover such as CLR or Lime Away. DO NOT ! MIX ANY OF THESE CHEMICALS UNDER ANY CIRCUMSTANCES! Try one making sure to give it time to work then thouroughly flush the toilet before trying another. The brown stain may be rust or water scale. If the porcelain is actually gone replacing the toilet is probably the only fix. Hope this helps.
Bob

Take some Ajax and lightly rub it on the stain just hard to remove the stain. The main thing is you don't want to etch the porcelain..