For most things I clean I run plain water in mine and all my parts are in a glass beaker that is lowered in the tank. I put my cleaning solution in the beaker.
Bigger items the above doesn't apply of course but for any small items it works really well.
If you buy a larger one a drain on the tank is really nice.
^^^ This! Except instead of beakers, I use glass jars with lids on them (mason jars or whatever your breakfast jam comes in, or glass quart milk jugs for long bolts). I use Evaporust on all of the steel parts on machines I restore. Evaporust can be diluted. So, all hardware goes into a glass jar with some Evaporust, some Cascade dish detergent (works great as ultrasonic soap---better than simple green in my testing), and then I put the lid on (no lost tiny washers/screws!). This way I use way less evaporust compared to filling the whole tank, and I can have different parts in jars with different solutions at the same time (or 'cleanish stuff doing final rinse' jar and 'filthy stuff' jar). Plastic jars work OK too but it depends---I have deformed them when running the heater.
Always use a basket---parts should NEVER touch the bottom of the tank, or it will damage your tank and/or transducers (which is why you see so many ultrasonics on ebay with messed up tanks).
My unit is a Crest 1.5 gallon unit, which is the biggest/heaviest I would want to go if I ever have to move it when full of water/parts (~25lb of machine + dirty boiling water + parts). I want a 7-gallon one too for bigger parts, but that one will stay put on the bench with the drain tube fed into a work sink.
Ultrasonics are 'annoyingly noisy'---not very loud, but the racket they make is annoying. I can be in the next room for extended periods of time, but only with headphones or a fan/something running to cover the noise.
