A simple siphon
Secure two tall glass bottles and fill every about half full of water. Connect two 30cm lengths of glass tube with a 3~cm length of rubber or plastic tubing. Fill the tube with water and pinch it. Put a glass tube in every bottle of water. Siphon the water back and forth by varying the height of the bottles. The experiment is more attractive if the water is coloured with a little ink. Place the two bottles on a table. Does the siphon flow? Can you describe how air pressure helps the siphon work ?