Abstract: A retainer assembly for locating a medical device in a container having a wall with a vent hole. The retainer assembly includes a retainer with an undersurface that is larger than the vent hole and an axial passage having a selected length and cross section extending into the retainer from the surface. The assembly also includes a keeper having a head that is larger than the vent hole and a sleeve extending from the head to an end. The sleeve has substantially the same cross-section as the passage and is shorter axially than the passage so that when the retainer surface is engaged to one face of the container wall so that the passage is aligned with the vent hole and the keeper is engaged to the retainer by frictionally engaging its sleeve in the passage until its head contacts the opposite face of the container wall, the retainer becomes securely, but releasably, anchored to the container wall.