My agency had an ultrasonic cleaner. If the ultrasonic cleaner is functioning properly, it only takes a few minutes to clean the gun. Letting the gun sit in the cleaner for a half hour or longer is not recommended. We field stripped the gun, put the metal parts in the sonic cleaner with a hot water-based detergent, dried the parts, then immersed the parts in a light oil bath. The light oil bath displaced any water that was still in or on the parts. Oiled the parts and reassembled the gun. We never had any problems with this procedure. The sonic cleaner did a really good job of cleaning the hard to access places in our MP5 SMGs and HK33s.