Simple Green. Safe to handle, natural, and won't melt plastic. Throw your models in a Tupperware container, pour Simple Green (enough to cover all models), leave it over night (few days for older models. Come back and rinse them with hot water in the sink. Use a toothbrush for scrubbing. Sooooooooooo much easier and less toxic than any other option.
Simple Green contains 2-Butoxyethanol, which is pretty harmful as a vapor. It seems to leave a slight smell of Simple Green on plastic figures. Simple Green can be flushed with no issues.Superclean uses Lye, which is corrosive on organic tissue. (Ironically Lye is used in food prep)They both work equally well, and the main choice is corrosive VS toxicity, lol!So between the 2 chemicals