When the water enters both sides of the tube it fills the volume within the given space. When she flips the tube over and the water is allowed to release at one end. The water pressure is created and begins a continued flow of water as the vacuum exerts just enough pressure to sustain the process. 

That it allows for the graceful pull, flow, and dispersal of water into an external volume. This process will continue until either an outside force stops it, or the water lever drops below the pipe entrance. Which will then cause the last of the water to be released simetaneously from both ends.