Think of the nozzle as you would a tee fitting. It has three openings; top, bottom and side.
The bottom opening has a rubber seal that creates an air tight seal to the bottle you’re filling.
The opening on the side gets a piece of tubing attached that runs into your clear wine, ready to be bottled.
This has to stay submerged for the vacuum to work.
The top opening gets a piece of tubing that is then connected to your vacuum pump.
The vacuum pump evacuates the air inside the tubing and the bottle creating negative pressure inside the tubing and bottle, which the wine rushes in to fill.
If you allow the bottle to fill completely, the vacuum pump will continue to evacuate the tubinh connected to the top and wine will rush up that tubing and reach your vacuum pump.
You need to break the vacuum before that happens.
Once the vacuum is broken, the wine will stay put.
You can break the vacuum by pulling the tubing out of your wine supply, or breaking the seal between the nozzle and the bottle.
Is that helpful?