Once both balloons are inflated, CO2 is used to insufflate the space between them. Because the rectal balloon is anchored against the anus and cannot be moved, the scanner balloon is propelled forward along the colon by the air pressure building up between the two balloons. [...]
Once the Aer-O-Scope reaches the cecum, the CO2 behind the scanner balloon is vented out through the rectum, and CO2 is used to insufflate the space between the scanner balloon and the bottom of the cecum. The workstation now establishes higher pressure levels in front of the scanner balloon, thus propelling the balloon and capsule back towards the rectum. This "reverse motion" may be supplemented by the operator gently pulling on the supply cable.
(Or, in layman's terms, "blow it out your ass.")