Hi Mike,
I am sure that Bernard will be in a better position to answer your questions (my only experience in ultrasonics are using ultrasonic probes to disperse PVC emulsions many years ago and,more recently, watching the effect of a small bath on my wife's jewellery).
However, I think it must be safer to reduce flammable volatiles content to a minimum in the cleaning solution (not sure that the IPA is even necessary to be honest) as the ultrasonics could cause fast formation of a flammable vapour around the bath.
The reason that I am not sure that IPA is needed is because the effect of cavitation together with a good surface active agent (emulsifier) would lift any dirt particles from the surface of the record and keep them in suspension.
I have been very interested in this thread - I just need to persuade my wife to let me buy a bath!
My only suggestion for improving the process would be to spray the cleaned record with distilled water from a "plant sprayer"? (perhaps IPA mix to speed evaporation?) to rinse off any remaining emulsifier at the end of the process.
Guy.
LP12, Ittok (black), DV10X5, NVA Phono 2 (twin supply), NVAP50, Art Audio Quintet 15w power amp, NVA LS5 cable, Rega Ela mk1's.
Sony CDP XB930.