In one of the other threads currently running
here, I asked about what they were using as a solvent.
They finally dug up the name, it's called Alconox.
I then ended up talking with a friend who does soil contamination studies, and he mentioned that they use the same stuff in VERY small quantities to clean their test equipment. (~1 Tbsp per 5 gallons of water)
The original posters of the other thread replied to my concern about the water as well. They were then removing the injector parts, drying them, and soaking them with oil to protect them.
From reading in other locations, I've gotten the impression that it's a bad idea to use anything flammable in an ultrasonic cleaner, particularly if it's a light solvent.
I'm not sure just how BioDiesel would react, but for me, I think I'm going to play it conservative in this.