A medical device has an interior for containment of fluids; an opening into the interior, an elastomeric wall comprising a fixedly placed, flexible barrier across the opening; and a retention wall positioned adjacent to a peripheral portion of the elastomeric wall. The retention wall defines a central opening and has a generally rigid retention zone surrounding the central opening, to engage and retain a connector tube which is advanced into the central opening to open a flow aperture through the elastomeric wall, for flow through the wall and connector tube. One of the retention zone and connector tube may be made of a material of sufficient hardness that material of the other engaging member is deformed by engagement therewith, which increases the strength of retention between the retention wall and the connector tube.