I use the ground walnut shells. Fill tumbler about 1/2 way with media. Dump in your cases, put top on and let them go for about an hour or so. The media will go inside the cases so when I take them out, I leave the tumbler on and as I pull out the cases I hold them upside down against the rim of the tumbler to vibrate the media out.
Be sure to clean the primer pockets as a lot of times the media gets lodged in the flash hole.
I clean my cases after sizing as I use Hornady One Shot as a lube. If you use the old lube like RCBS, you may want to clean prior to sizing as the lube may contaminate the media.