I have one toilet that works fine, but the bottom of the bowl looks like those you see in gasoline station restrooms. I can scrub it with a toilet brush and a dose of bleach and most of it clears up, but the bottom still looks stained. Is it that the china has gotten old and is retaining stains? A woman told me that it is because of the wax ring, but I doubt that. I was thinking may a paint store would have an epoxy that would fix the stain. Would that be the way to go?