Here's what I have to say about ultrasonic cleaners- The way they work is by pounding the parts with shock waves that they can feel, but, for example, your fingers can't. The same technology is used to pound kidney stones to smitherines inside your body when you sit in a tub of water that's subject to the same waves.
As I understand it, tap water has dissolved air bubbles that absorb the majority of the shock waves, so, by using room temp, or even hot tap water, very little energy goes to the gunk. Instead, the energy is absorbed by the small air bubbles that are in the water. The thing to do, (again, as I understand it) is to boil the water for a few minutes so that the dissolved air bubbles are boiled out of the water. This is the same reason why boiled water makes clear ice cubes, and tap water makes cubes with opaque air bubbles in it...
When you use previously boiled water in an ultrasonic cleaner, it works, WAY better than when using tap water. You can see this easily in real life. I simply use a few drops of (laundry) detergent (NOT soap) in about 2 cups of boiled water, and it cuts through greasy dirt better than gasoline!