Stick a hose up through the hole and make it watertight.
Fill the pail 3/4 full with sand.
Place a heavy object on top of the sand. The object will stay put.
Turn on the hose so that a little water trickles up through the sand. The sand will swell and grains will pull apart. When there is enough water to make the sand "quick", the object will sink.
Turn off the water. The sand will settle and water will come to the top. The sand can now hold another heavy object. This is because the water is squeezed toward the top, and the grains of sand aren't pulled apart as much.