How is this done?

[ron101]

Originally Posted by lastlight

if you placed a mostly full pop bottle of water into the sink upsidedown quickly, the water would stay in the bottle. Could you not then have an air pump with the input inside the bottle drawing from that air cavity at the top? Blow this air into the bottom of the bottle so it just goes right back where it came from?

Yes but I would be concerned about eventual oxygen depletion from recycling the air. Although there may be enough gas exchange from the 'open' areas of the tank.