There was a thread in here asking how to remove reddish brown stains from a toilet bowl. I suspected the stain was iron oxide from the houses's water supply plumbing, and so I told the poster to use a hydrochloric acid based toilet bowl cleaner. But, I got this tip from a website that caters to the janitorial industry (www.cleanfax.com) and I thought it was a good one, so I wanted to pass it on. Restaurants use this to prevent their toilet bowls from smelling if someone doesn't flush: After cleaning the toilet, what's really good practice is to kill the bacteria in the part of the bowl you can't get to with toilet bowl cleaner. After cleaning the toilet and rinsing out the cleaner, empty the bowl and pour bleach straight out of the jug into the bowl to the normal height the water level in the bowl. (Any additional bleach you pour in will simply pour out of the toilet into your drain piping, so pouring more in is just wasting bleach.) Allow the bleach to sit in the toilet bowl for at least 15 minutes, and then save that bleach for the next bowl cleaning. The bleach will kill all of the bacteria in the toilet bowl that feed on human waste so that the bacteria don't start to multiply if someone uses the toilet without flushing. And, of course, preventing the bacteria from growing and multiplying is how to prevent your toilet from smelling.