The inside rim of the toilet bowl tends to get a black rim around it, as well as below it. Not sure if I am describing this right, but I think it comes from my son's aim, but not sure. The bottom of the toilet seat has some pee stains on it as well. I tend to use vinegar and water for cleaning, and it does not quite do the trick here. Part of the reason is its hard to get under the rim, but its not doing great on the parts I can get to either. What do you use? Thanks!