I have the STM 17 pound model which is similar to Thumlers but the shafts are 1/2 inch and the bearings are sealed ball rather than plastic bushings. Also will handle more brass.
I got the kit which includes a separator. If you fill the bottom half of the separator 2/3 to 3/4 full of water and spin the cage full of brass IN THE WATER 99.9% of the pins will be out in 10 rotations.
If you spin the brass damp, not immersed, water surface tension holds the pins inside the brass.