Are you talking about an ultrasonic cleaner? Which one? I have the larger harbor freight unit and after researching what others have used, this is my method (I wasn't impressed at all with the HF cleaning solution stuff):
Fill the tank with water about half way.
I do small amounts at a time (50 .223 cases for example.
I divide the cases into 2 ziploc bags
I put a 50/50 solution of white vinegar and water with a drop of liquid dish soap in each bag - enough to cover the shells easily.
I seal the bag as I squeeze out as much air as possible without making a mess.
I set the cases in the solution with the machine on.
There is a sweet spot of sorts that I have to figure out with the machine. If the water level is close but not over then I am good and I hang the bags over the sides and adjust them up and down to hit the sweet spot - the water in the tank almost boils at the right spot.
I turn on the heat and set for 480 seconds and let it go. When done, I agitate a little and switch the bags around.
When the second cycle is done, I drain off the vinegar solution for reuse and dump the shells quickly into water with baking soda to neutralize the vinegar.
Rinse and dry, run through the tumbler for a nice shine and they are good to go.
Hope this helps. I did a search on ultravib and came up with a Thulmers dry media tumbler. That didn't sound like what you have. Good Luck