An adapter for use in connecting a vacuum source with a breast shield is disclosed including a housing with at least one female coupling component formed therein, at least one male coupling component that is adapted to attach to a tube at one end for conveying pressure from the vacuum source, while the other end is sized and shaped to be received in the female coupling component. A passageway extends between the first end and the second end of the male coupling component for conveying the pressure. The female coupling component is defined therein by an interior sidewall that has a channel formed therein open to the female coupling component at least somewhere along the interior sidewall. When the male coupling component is inserted in the female coupling component, a sealing portion of the male coupling component engages the interior sidewall surface. A stopper is provided to effectively permit the use of only one of a pair of female coupling component.