To make it work, just put some dry ice in the bucket, add warm water. Snap on the lid and watch the kids freak out! This video was taken about 4 minutes after the water was added. The vapor shot out further earlier on. As I said before, to reinvigorate all you have to do is add more hot water and/or more dry ice.
notes on dry ice-
Dry ice is just frozen carbon dioxide. The "smoke' you see is just water vapor and is not harmful or toxic.
The only way the carbon dioxide can hurt you is if you displace the oxygen in a small enclosed space.
However, the ice is very cold (-109 F!!!!!) and will actually cause burns to your skin. You could pick up a chunk of dry ice and as long as you bounce it around like a hot potato you will not get burned. UNLESS your hands are wet, in which case it will burn you almost instantly (trust me) Plan on wearing gloves.
If you have to store the dry ice for long. Store it in a large cooler and wrap the cooler in sleeping bags and blankets. Don't think you are going to get more than 24 hours without having a substantial amount of your dry ice literally vanish into thin air.