I use Nu-Finish with walnut media only, some people use combo of walnut & corn cob media?????
My brass always comes out better than new. ( Which isn't always hard to do )
As far as dust, I use used drier sheets when available (we have not been using them lately ).
Plus a few other things I have tried that work ok. ( working OK means when I take the material or sheet out of the tumbler, it has dust attached to it )
I also have successfully used cut up paper towels, better than that is what I think is called "backing" that is used to back material used in making clothes. My wife sews and uses this stuff and I always grab the scraps and save them for my tumbler.
It comes in a Bolt like clothing material does, or you may be able to find small pieces at Walmart or JoAnns or Clothworld or other material/sewing stores??? Its pretty cheap and works OK. It pretty much looks like drier sheet material..!!!
Sometimes I have seen it under the bottom of cloth covered large living room chairs or even on the bottom of couches/sofa's.
Just try cheap stuff like that and see if it works, if so..GREAT...if not, keep looking

Anything to trap dust particles and then throw them away.
Don2
Ps..I did a test years ago before using Nu-Finish on my brass, I used nu-finish on some throw away 30-06 brass, then hung them in my shop for almost a year while I was rebuilding it "The shop"....After that time, it was still looking fine inside and out and brass was not discolored or any way looking bad. It was just my little test before I committed to using and keep me from worrying about ruined brass.