As far as using my ultrasonic cleaner, I use just lukewarm water and this is my exact procedure:
The first thing I do is make sure that I have a good resistance reading with a multimeter and it's usually 2.1 to 2.8 mA so I know it is still a working atty. If your atty is not working at all and the resistance is way high, then it probably is dead, but I would at least try one good cleaning just to be sure.
I blow out my atty from the open (cartridge) end really well. Then drop it into my ultrasonic cleaner with lukewarm tap water for 8 minutes. I take it out and flick it with my hand to get out as much water as possible, then blow it out again from the cart end really well. I then set my atty to dry which for me is on top of my pellet stove which doesn't get too hot to touch (the cats sleep on it), I'm sure a radiator or baseboard heater or heater vent or even on top of your boiler would work just fine. By the next day it is good and dry.
I then put it on my NicoStick at the standard 3.7v and begin my dry burn process. I push and hold the button for about 5 seconds, release and then blow into the atty to cool it down. Once I begin to see an orange-to-red glow, then I push and release the button for about a second and continue this
off - on sequence with brief heat up and release so that my atty does not get bright red and risk overheating it, but no more than 7-8 seconds total time. I'll continue this perhaps 3 or 4 times. Then I'll hit it one time for about 3-4 seconds and get a nice red glow and I'm done.
Then it's back into the ultrasonic cleaner for 2 - 8 minute cleanings. Each time I use the cleaner it heats up the water a few degrees by itself. The cleaner does not have a heater, but the sonic action in the water (the collision of the water molecules you can actually see) heats up the water. 4-5 uses at 8 minutes each and the water starts to get hot. Pull out the atty, flick it out, blow it out really good and back on the pellet stove to dry. The next day it is like brand new once again.
Everyone has their own cleaning method and this works for me.
I got my ultrasonic cleaner
here for only $31.95 and it costs me $10 for shipping and I use it for cleaning up all kinds of stuff.