You are never going to get rid of every little spec of media from tumbling. The good news is that walnut and corn cob are really soft and don't damage anything. Annoying at worst.
I use a collander that I drilled out the holes bigger and dump my vibratory bowl in. It fits perfect in a bin I have so I can slide the collander back and forth until the majority of the media has sifted out. I use the chef's flipping the egg/pancake trick to sift out the remaining media. Never had much of an issue.