I use sisal twine to "floss" the cassette. It's cheap and the thickness and texture of the twine really grabs the gunk. Cut 4 or 5 foot-long pieces and get flossin'. As mentioned above, if the cogs are really dirty a light misting of WD40 really cuts through the grime. Shiny clean in no time!


+1 on Chain-L for a silent drive chain.