I also have to clean the red dust off my cases tumbled in Lyman walnut media.
Beware the red dust most certainly contains lead residue from primer compounds, and you could be inhaling it. Make sure you wash you hands after touching it too.
As the media gets older it seems to get dryer and has more pices ground into dust, eventually this will cover everything you own near the tumber. The media isnt worn out, you just need to get the dust out if you want to keep it, washing to pouring while letting the dust blow away all work.
After buying a second used tumbler that appears to have corn media in it I have just been using it lately, or a Lee Zip Trim with steel wool.