Procedure:

1.	Punch a hole in the side near the bottom of the bottle with a small nail.
2.	Fill the bottle with water and show the leaking container to your parent.
3.	Ask: "How can I stop the leak without wetting my finger?"
4.	Put the one-hole stopper on the bottle and cover the hole with one finger: the leak is stopped!
5.	Release your finger from the stopper: the leak will start again.

The water does not stop flowing immediately after covering the stopper, but it still keeps dripping out of the bottle for awhile. This increases the volume of the air pocket above the water. The amount of air stays the same because air is prevented from coming into the hole in the stopper. The increase in volume causes a decrease in pressure (Boyle's Low). The outside atmospheric are pressure pushes against the water and prevents it from flowing out. This is why we always punch two holes in a can of evaporated milk to pour the milk out. In large gasoline containers you may have noticed the small sealable vent opposite the pour spout. This hole will allow air to enter the can as the gasoline is poured out. It will promote a smooth flowing of oil out of the can.

Follow-up:

1.	Why did the water stop flowing out of the bottle?
2.	How could you stop the leak of the the lid with the hole was missing?
3.	Does the water stop flowing immediately after the hole is covered??
4.	How does the air pressure inside the can compare with the atmospheric pressure air pressure after the water stops flowing??
5.	What is it that we prevent from entering the can by covering the hole??
6.	What purpose is served by the small vent in a gasoline?