+1 on the Ultrasonic cleaner. Small ones can be had fairly cheap -- enough to accomodate a slide/barrel/etc. from a handgun. You can simply use water as the solution in the tank. Hit everything with WD-40 afterwards and wipe clean. Hit moving parts with a little oil, and it's ready to put away.
I'm sure they exist, but one large enough to clean a long gun would probably be REALLY expensive.
I'm sure they exist, but one large enough to clean a long gun would probably be REALLY expensive.