System 2 is a closed glass container. Air to replace the volume of fluid passing through the tube to the air filter to the air through the mouth of a bottle of liquid.
The system is a closed system, 2 glass containers, air will pass through the liquid volume substitution is used to pipe air filter air bottle mouth area thus through liquids.
The system 2 is a system off container is glass bottles air will pass through the liquid volume to replace air filter used to go through the pipe mouth air, through the liquid.