I also use my USC for cleaning chains before taking them to my Oregon 520 to sharpen. I use old "2-stroke solvent" that's been in the can too long to risk putting in the saws. Put the chains in a mason jar with the "solvent" and drop it in whatever regular cleaning solution happens to be in the USC at the time. I've never had a problem, but I carry the thing far out into the driveway and plug it in with a long extension cord, in case anything ever decided to go "pyrotechnic" on me. I DO NOT RECOMMEND THIS PRACTICE TO ANYONE! FOLLOW THE INSTRUCTIONS THAT CAME WITH YOUR USC! I AM AN FULL-BLOWN IDIOT, AND WILL NOT BE RESPONSIBLE FOR ANYONE NOT FOLLOWING THE MANUFACTURER'S MANUAL THEY RECEIVED WITH THEIR ULTRASONIC CLEANER! In 10 minutes or so they look like new; this strips the tree sap and bar oil crud off the chains that will clog and glaze a grinding wheel in a heartbeat. I then hang them on a nail and blow them off with compressed air before grinding them. After sharpening, I mist them with whatever penetrating oil I've got handy for rust prevention, and drop then in a zipper bag for storage until they go back onto my saw, or back to the owner.
I know most people exclusively hand file their chains, and certainly I respect that. It's easily the fastest way to touch up a lightly dulled chain, but it's a lot of work on a heavily damaged chain that needs some serious material removed to be anything close to right again. I'll often give a tooth a quick lick with a hand file to knock the burr off after grinding anyway, and make sure that point catches my fingertip like a cat's claw while it's still locked in the tooth vice of the grinder.
I would love to try square-filed chain someday, but I probably never will. I've got steel pins, plates, and screws in both wrists, and all the vertebrae between my shoulder blades previously broken and repaired, so I'm not very interested in hand filing ANYTHING. I'll make do with what I can do, just don't flame me too much about grinding chains before you've walked a mile in my shoes is all I ask............