Kung Fu Maintenance explains how to get rid of stubborn nasty stains and rings in the toilet.
So you clean your commode with a toilet brush use lots of chemical but no matter how much elbow grease and cleaning product you use you are still stuck with an ugly ring. What you need here is a pumice stone. If you have an epoxy colored toilet or have any doubt if the pumice stone might scratch the toilet than test it first, either inside the tank, or on the bottom, or back of the tank where it will not be seen. Wear two to three pairs of disposable latex gloves. Unwrap one end of the pumice stone and use it with your favorite bowl cleaner to rub out the ring. It is a soft sanding stone and it will not scratch your porcelain but with a little effort it will remove even the most stubborn stains. Back track your outer glove over the remaining pumice stone wrapping it up to save it for another round. Now your toilet looks more like a throne.
~~~Maintaining the Throne~~~
~~~~~~~~~~Kung Fu Maintenance~~~~~~~
Chapter 6 artwork diagram from the book Kung Fu Maintenance