I have to admit, I was a bit concerned that ETI was using a "plastic" toilet in their builds, when I have had a china toilet in my Scamp all these years.
But, I've heard enough good things about the reasons "why" I'm no longer concerned. So, you don't use a pummis stone to remove the ring.. you wax it instead!
And if you think I'm kidding, I'm not... there are threads on RV.net that talk about waxing the pot. Honestly tho, they talk about using stuff like RainX(?)