What it shows:
With an air pressure of 10⁵ Nm^-2 at sea level, even a heavy duty oil drum will be crushed if it has nothing inside to balance the pressure.

How it works:
The screw cap on the drum is fitted with a vacuum pump connector. Simply turn on the pump and wait; it takes about 8 minutes to pump down, so you can carry on with what you were doing interrupted by various creaks and bangs as the drum's side walls begin to give. Because drums of this size are ribbed for strength, they can hold up under the strain, but when it finally goes it collapses with a mighty implosion! 35 gallon drums are more robust, but a sharp thump with a mallet on the ribbing is enough to remove any last resistance and a loud instant implosion follows.

Setting it up:
Because the drum takes a few minutes to pump down, it's a good idea to have the pump outside the hall so the lecturer can still be heard; the drum being just inside the door. Provide a rubber mallet.

Comments:
Can be done with any size drum you lay your hands on; obviously it is important to check the previous contents, to avoid toxic or corrosive residues. A smaller version can be done with a one gallon oil can and a Bunsen burner replacing the vacuum pump. Boil quarter of a can-full of water so that the steam replaces air in the can. After you're sure it's purged, take it off the heat and screw the cap on tightly. As the steam condenses, a vacuum is formed and the can will crumple. Here you haven't got the possible misconception of the can being 'sucked in' by the pump.