Abstract: A device useful for draining fluid from the pleural cavity of a patient includes two enclosed chambers. The first chamber has at its upper end a one-way directional valve. The valve, which is provided with a connector for connection with a catheter draining fluid from the patient's pleural cavity, operates only to allow fluid to flow into the first chamber. The lower end of the first chamber, which is releasably connected to the second chamber, is optionally provided with a second one-way directional valve that operates only to allow fluid to flow from the first chamber into the second chamber. The second enclosed chamber of the device of the invention has an upper end and a closed lower end. The upper end of the second chamber is releasably connected to the lower end of the first chamber to provide a substantially fluid-tight connection. The device is provided with an outlet to the ambient atmosphere; the outlet can be disposed in either the first or the second enclosed chamber.