Have you ever fooled with a ultrasonic water mister? If so, you'll know that the mister must be placed a certain distance from the surface of the water. Drop one in a deep container, and it doesn't work. If the water is too shallow, it won't work either. Now here is the kicker---the mister consumes water during its operation. That means that the level of the water in the container will change. The easiest way I've found to make a robust mister set up is to use a float that holds the device at the proper depth.

The .STL file here works for Spirit plastic version. Aluminum based versions require that you stretch it a bit (3mm bigger should do it).

PLA, Wall thickness=2, infill percentage=05, Supports=Yes, Time to print on MonoPrice Maker Ultimate2=4:46 hrs, Filament=70g