A device and method to constrict or occlude the lumen of a flexible tube may include an occluder under the influence of an elastic force, such as a spring force, that can compress a portion of the wall of the flexible tube. The occluder can be under the influence of the elastic force, but prevented from occluding the tube by a stop. The stop can be connected to a tube gripping feature, so that a pulling force on the tube near the gripping feature can disengage the stop from the occluder, releasing the occluder to compress the tube. In some embodiments, the pulling force applied to the tube causes movement of the gripping feature by taking up slack in a portion of the tube held in the device. In other embodiments, the pulling force applied to the tube causes the tube to stretch elastically near the gripping feature, causing the gripping feature to move, and disengaging the stop from the occluder.