Clog resistant air vent plug for teatcup liner

An air vent plug (70, 90, 94) is provided for insertion through the wall (12) of the milk tube portion (14) of a teatcup liner (16) used with a teatcup assembly (18) for milking a mammal (20). The air vent plug has an outer flange (72) exterior of and engaging the outer surface of the liner, a barrel (74) extending through the wall of the liner, an inner tip (76) interior of the liner, and a vent passage (78) extending from the outer flange inwardly through the barrel and the inner tip. The vent passage has a first calibrated diameter (80) at the outer face, and a second larger formed diameter (82) inwardly thereof. The different diameters meet at a transition shoulder (84) which faces away from the air inlet opening (87).