The volume of the apparatus must be about the size of a coffee can, so use an actual coffee can. Dropping the coffee can might damage it, so it would be prudent to have some spare cans on hand.
Fill the coffee can with water. Dissolve salt into the water until an egg placed in it will float.
Drop the water-filled coffee can with the egg floating in it from 4 meters and see if the egg survives. Keep increasing the height of the drop until the egg breaks, then back off half the distance higher than 4 meters. For example, if the egg finally breaks at 14 meters, then back off half of the extra 10 meters, for a total drop of 9 meters.
You'll need to devise some way to maintain the orientation of the coffee can as it drops so it doesn't turn sideways; maybe you could glue some fins to it, or drop it inside a hollow tube, or... I'm sure you can think of something better than that, though.
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