I had a whole bundle of rather badly painted Gaunts from my early days in the hobby and thought it'd be a good idea to try restoring them to grey plastic, with the intent of repainting them better. To do this, I took my ultrasonic cleaner and used a roughly 3 parts lacquer thinner to 7 parts water mixture to fill it with, before dunking the models into the thing to soak for a bit. Lid on, button pressed, waited a bit...
...Returned to find the diluted thinner was still strong enough to melt not only the paint, but also the plastic of the miniatures AND THE PLASTIC BASKET INSIDE THE CLEANER.
I'm currently letting the cleaner and its contents soak with water in the hope of at least avoiding any further damage to the cleaner. I suspect the Gaunts are toast (or rather, syrup) at this point though. Fortunately they were not a great loss, as they were painted thicc, but even so. Let this be a cautionary tale not to use lacquer thinner as a stripper, even diluted.
With that being said, what's a good thing to put in an ultrasonic cleaner to strip miniatures without turning them into mush?