I do my Sharpmaker rods in 2 stages. First of all I get the worst of the engrained metal off with either Ajax or Comet. Then rinse them off in very hot water. Then for the second/final stage I use a product you can get here in most of the USA known as Bar Keeper's Friend. It's a scouring/scrubbing powder you can find in my grocery stores, hardware stores, family dollar type stores and at good old Rip-mart. It's found in the same part of the store where they sell the comet and Ajax
I then use ScotchBrite pad with a lot of Bar Keeper's Friend and I scrub it vigorously and then rinse them in hot water. After those 2 stages the rods/stones are very clean and ready for work again. And after a cleaning that thorough they really cut uniformly again.
That's the method that has been working great for me for over 5 years now. IF anyone has a better method than that I would be more than willing to try it out.
I've tried the pencil/ink eraser method and it does get a lot of the filings removed and I won't argue that but the stones just don't abrade as uniformly as they do when you give them a really thorough cleaning like you can do with a regular scrubbing powder and Bar Keeper's Friend cleaning powder. Good Luck