Acutally since you asked..... I have used "Dry Wash and Guard" inside my toilet bowl. drain all water, make sure it is dry inside bowl. Apply dry wash and guard as per directions with the spray. Dry it out with a paper towel. This acts as a slick surface and helps eliminates skid marks inside the bowl. We now have a porcelain bowl and this is not necessary. Why is it that RVers almost always revert to " black water" discussions?
We have used Protect-All (similar principle to Betty's Dry Wash) in toilets to make them slicker and less prone to skid marks, water spots, etc. Helps keep sinks & showers clean too. It has to be re-applied occasionally, but it definitely helps.