designed to sealingly wipe against the outer diameter of a first or small vent pipe the diameter a preferably is on the order of 1 25 inches to 1 35 inches and is distensible to accommodate the outer diameter of 1 25 or 1 5 inch nominal inner diameter vent pipe as a first primary seal a first secondary seal is accomplished by distension of a first secondary shoulder 18 which has a nominal diameter b the preferred value for diameter b is 1 5 inches to be distended by a nominal 1 5 inch vent pipe outer surface in the event a 2 inch vent pipe is to be used a frangible separation of the first annular ring 8 is made along the second separation circle 9 to define a second primary seal of a diameter c the preferred value for diameter c is 1 75 inches so that it will be distended substantially by the outer diameter of a nominal 2 inch inner diameter vent pipe a second secondary seal for a 2 inch vent pipe is accomplished by distension of a second secondary shoulder 20 which has a nominal diameter d the preferred value for diameter d is 2 0 inches in the event a 3 inch vent pipe is to be used second annular ring 10 is separated along the third separation circle 11 to define a third primary seal of a diameter e the preferred value for diameter e is 2 5 inches a third secondary seal for a 3 inch vent pipe is accomplished by distension.