An apparatus configured to provide positive airway pressure in a respiratory circuit comprises a container configured to be filled to a preselected level with liquids a drop tube assembly comprising a hollow gas tube rotatably mounted in said container having an upper end extending a static distance outwardly of the container and connected to a respiratory circuit downstream of a user, and a hollow drop tube reciprocally movable upwardly and downwardly in the liquid in response to rotational movement of the gas tube. The container is provided with a gas vent and a liquid fill port.
