A connector comprising: a housing having an internal cavity with a first port, a second port, and a fluid path from the first port through the internal cavity to the second port; and a plug having a first position and a second position within the internal cavity, the plug configured to block the fluid path between the first port and the internal cavity when in the first position, the plug comprising: a plug neck having a face; a diaphragm configured to separate the internal cavity into a first volume that is vented and a second volume that includes the fluid path; a biasing element disposed within the first volume, the biasing element configured to urge the plug toward the first position; wherein displacement of the plug from the first position toward the second position opens the fluid path and increases the second volume; a shoulder that contacts the housing and separates the second volume into a third volume between the first port and the shoulder and a fourth volume between the shoulder and the second port, respectively; and a passage from the fourth volume through the plug to the third volume, wherein the passage is open when the pressure in the fourth volume is greater than the pressure in the third volume to allow the pressure in the third volume to increase to the pressure in the fourth volume, the pressure increase in the third volume exerting an upward force on the plug neck to create a tighter seal between the face of the plug neck and the first port, and the passage is closed when the pressure in the fourth volume is not greater than the pressure in the third volume. a housing having an internal cavity with a first port, a second port, and a fluid path from the first port through the internal cavity to the second port; and a plug having a first position and a second position within the internal cavity, the plug configured to block the fluid path between the first port and the internal cavity when in the first position, the plug comprising: a plug neck having a face; a diaphragm configured to separate the internal cavity into a first volume that is vented and a second volume that includes the fluid path; a biasing element disposed within the first volume, the biasing element configured to urge the plug toward the first position; wherein displacement of the plug from the first position toward the second position opens the fluid path and increases the second volume; a shoulder that contacts the housing and separates the second volume into a third volume between the first port and the shoulder and a fourth volume between the shoulder and the second port, respectively; and a passage from the fourth volume through the plug to the third volume, wherein the passage is open when the pressure in the fourth volume is greater than the pressure in the third volume to allow the pressure in the third volume to increase to the pressure in the fourth volume, the pressure increase in the third volume exerting an upward force on the plug neck to create a tighter seal between the face of the plug neck and the first port, and the passage is closed when the pressure in the fourth volume is not greater than the pressure in the third volume. a plug neck having a face; a diaphragm configured to separate the internal cavity into a first volume that is vented and a second volume that includes the fluid path; a biasing element disposed within the first volume, the biasing element configured to urge the plug toward the first position; wherein displacement of the plug from the first position toward the second position opens the fluid path and increases the second volume; a shoulder that contacts the housing and separates the second volume into a third volume between the first port and the shoulder and a fourth volume between the shoulder and the second port, respectively; and a passage from the fourth volume through the plug to the third volume, wherein the passage is open when the pressure in the fourth volume is greater than the pressure in the third volume to allow the pressure in the third volume to increase to the pressure in the fourth volume, the pressure increase in the third volume exerting an upward force on the plug neck to create a tighter seal between the face of the plug neck and the first port, and the passage is closed when the pressure in the fourth volume is not greater than the pressure in the third volume.