The white hose nearly touches the bottom of the inside of the container. While the tank fills also the hose fills. At some point, when the container is nearly full, the hose is full of water and start to siphon the water out of the container. The white hose is larger than the blue inlet hose, so the container empties faster than it fills.

The tank empties, santa is heavier than the container: The tank goes up, Santa comes down.