Set the propane burner on the ground, and place the propane tank next to it.
Connect the propane tube from the tank to the burner by turning it clockwise, but do not open the valve on the tank until you are ready to ignite the burner.
Place the pot on top of the burner, and fill it with water to within 6 inches of the pot's top.
Place the China cap on top of the pot. A China cap is a large metal cone with perforations in it, and it is available at restaurant supply shops. The China cap should be placed within the top of the pot, with the cone pointed downward, sitting in the water.
Turn on the gas valve by turning it counterclockwise, and light the burner with a barbecue lighter. When the water begins to boil, place the clams in the China cap and cover the pot with a lid.