Well this took an odd and unpredictable turn....
I bought one of these guys several years back, pretty sweet. You can buy the soap at HF as well, (at least you could when I got mine) although it's probably not as good as a name brand soap.
It says not to use anything but water and the soap, buuut... I really have been itching to try some mild acidic oil mixtures/Machining oil and see what happens...
Just a note, in case you didn't know. Never put your hands (or any part of your body, Exarach) into an Ultrasonic Cleaner while it's running. It will damage the cartilage in your joints. (although, probably not as severely with the HF one, I've noticed it's not as powerful as the expensive ones)