If bleach doesn't work to remove sulfur stains from the commode, try using dishwasher detergent. It is formulated to remove stains from porcelain and is safe. Use about three times what you would for a load of dishes, let it sit for an hour, then scrub.
I use a product called Rust Aid from Lowes. I pour about a pint into the toilet bowl and leave it set overnight. The next morning it is bright and shiny like new. Use more as needed for tougher stains.