Best I can tell from watching the videos (and trying to figure out its function myself!) the spout coming off the flange has those 2 plastic nubs, which lock into the motor/battery unit- and they can be pulled away from each other, which would create the suction. So the vacuum is created right on that second part, and the milk is expresse then transferred into the storage bags with a one way valve. Let me know if this looks correct! This is only my best guess :p