my tenant just moved out and I found the bottom of the toilet bowl covered in a thick rust coloured grime. I tried bleach and scrubbing with toilet brush but it will not come off. I know there are many toilet cleaners on the market but not sure what will work for something like this. Any suggestions?

thanks.

any good bowl cleaner should work.remove the water and fill the an acidic cleaner and let it set overnight.
even muratic acid be careful not to splash back in face.