I have white toilets; I believe they are porcelain, but I'm not sure (I'm a renter). A ring appeared in the toilets at the top of the water. I poured a bucket full of water into the toilet to get the water level very low. I used a scrubby sponge and Comet to remove the ring, which worked for the most part. But the scrubber wasn't scrubby enough to remove it 100%. I really hated to leave it not quite clean enough, so I used what I thought was steel wool on just a few small spots. I actually read the box afterward and it was a stainless steel cleaner from Brawny. It must have had chemical or product on it because even though the rest of the ring was removed, it left a gray stain in the toilet bowl. Interestingly enough, it only stained the bowl exactly where the water always is, not above. I tried more Comet to remove the gray stain which did not work. Then I tried bleach, which also did not work. I searched the internet and found nothing; apparently no one is as foolish as me! Any advice?