The Argyle Thora-Seal III chest drainage unit (CDU) is a wet suction CDU used to reestablish negative pressure within the pleural space. It incorporates a replaceable collection chamber for monitoring volume, rate, and nature of drainage; a water-seal chamber that acts as a one-way valve, as well as a window into the patient's pleural space; and a suction control chamber to regulate suction and help re-expand the lung.