Try using some mineral spirits in the dry media. Add it before the brass and run it for 15 minutes or so to distribute it. Then run the brass.
See if that does the trick for cleaning. I've found it does help plus keeps the dust down, which is also important to me.
For really clean/shiny brass add some polish to the media. From time to time I'll add some Dillon's brass polish along with the mineral spirits. Don't need a lot of either, a splash of mineral spirits and a small dollop of polish, and good to go.
45_Colt