Summary: Vacuum is applied to an empty gas can which is then collapsed by atmospheric pressure.
Metal gas can
Rubber stopper with glass tubing to fit can
Rubber tubing and connection
The gas can is fitted with the rubber stopper and then attached to the vacuum pump. As the can is evacuated it collapses.
As an alternative, water can be placed in the can, and then the can is heated. Once the water is boiling, remove the can from heat, seal the can. Immerse it in cold water and the can will collapse