Insert the open end of a balloon through the copper tube on the bottom of an inflation chamber lid and secure the open end on the other side of the tube on the top of the lid. If needed, use a pen to push the balloon through the tube. Then attach to the container part of the vacuum unit, e.g., pull the mouth of the balloon around the end of the copper tube on the outside of the lid.
Have the kids pump the air compressor to remove air from the vacuum chamber to inflate the balloon.
If the vacuum chamber leaks, use some Vaseline and Q-Tips to coat the rim of the lid to ensure a better vacuum seal.
Place the funnel in the mouth of the inflated balloon. Take a 5 oz cup and fill it up 2/3 of the way with sand or rice. Hand the cup to the child and let them slowly fill up the funnel with sand.
Remove the balloon from the tube and tie off the balloon.
The kids can decorate their stress ball with the markers if they wish.