The water pressure inside the water chamber rises and the check valve, which is normally closed, is pushed open to allow water from the water chamber to enter the air chamber.
The water pressure in the water chamber drops, the check valve closes and the waste valve reopens.
The opening and closing times of the two valves are almost identical. (The sound of a rocket coming from the opening and closing of valves) At that time, the remaining water from the water chamber flows out through the waste valve. This is a continuous process and the water entering the air chamber can rise to the top through the outlet pipe under air pressure.