I do it the same way I cleaned locomotive wheels back when I ran DC. I use Goo Gone squirted on 3" wide strip of paper towel laid across the rails. I run the locomotive onto the towel holding it back while the drivers spin. After a couple of revolutions I back it up and run it back on to another area of the wet strip. Do this several times until there is no more crud coming off the tires. Then I make a last pass over a clean dry area of the paper towel. You'll be amazed how much gunk comes off those tires.
Ed Rappe