Abstract: An occluding collector is a housing with two tubular members adapted to be inserted into a duct carrying a biological fluid. A biological fluid passageway is provided within the housing between the two tubular members. A flexible member is operable to selectively close or open the biological fluid passageway in response to a fluid operating pressure in a catheter. In a preferred embodiment, the flexible member is a diaphragm which is movable to a convex condition for closing the biological fluid passageway and retaining the closed condition in the absence of sustained operating fluid pressure. The diaphragm may be moved to a concave condition for opening the biological fluid passageway in response to suction or partial vacuum created by retraction of some operating fluid. The diaphragm also retains its concave or open condition until again acted upon by the operating fluid. When the biological passageway is closed, the biological fluid may be drained or collected through a second catheter.