That is a small Harbor Freight cement mixer (1.25 cubic ft IIRC). I had to modify the mixer to allow the bucket to fit (yes, 5 gal). I "pie cut" the opening in the mixer and then bent the "slices" out to allow the bucket to slide in, the tension of the opening holds the bucket in place. I also glued 3 strips of pvc to the inside of the bucket to act as agitators. I use 1 gallon of water, as squirt of Zip clean and wax, a sprinkle of lemishine and let it run for about an hour. I separate the pins from the brass in a regular media separator filled with water (otherwise the pins stick in the cases) rinse and then let the brass dry on a towel, it's faster in the summer when I can set them in the sun, but even in the winter, they dry in a couple of days. I use the smaller pins and usually clean 2000 to 2500 cases per load (I could clean more but it gets really heavy to rinse and separate the pins). I started out using a vibratory tumbler, was too slow. Then I used ultrasonic, again, limited number of cases and the tarnishing problem appeared. I wanted to get away from the dry media tumbling because it was too much work. I saw an episode of "Shooting USA" where Jerry Michulek was cleaning his brass with a cement mixer (full size) and drying them in a commercial oven. I didn't need the volume of brass that he did, but I liked the idea. I saw the mini cement mixer one day and the rest is history.
Picture below is one load on my drying table, total time invested is less than 1/2 hour (I do something else while it is tumbling, so I don't include that time into the equation).
Also, brass that is not completely clean, or dry will tarnish faster as well. This is the reason I always clean and once polish all brass. JMHO 
