I fill my tank up so there's no air in the tank. During inversion the reels slide up and down within the fluid (there's head-room in the tank) but there's no air to trap. I've had no air bells with this technique. The tank is an Omega and I use stainless steel reels. These have plenty of opening between the layers of film so it's difficult for air to become trapped. I knock the tank down onto the bottom of the water bath after each inversion.(posted 8983 days ago)