A binary connector intercouples a plugged drug vial and a plugged, flexible-walled diluent container so that the diluent can pass to the vial from the container only after the latter has been pressurized by squeezing. Sharp-tipped, hollow spikes with intercommunicating axial bores extend in diametrically opposite directions from a disk-shaped base, with jaws having circularly arrayed flexible arms extending in diametrically opposite directions from the base, coaxially around respective ones of the spikes. A compressible rubber plug is wedged in one of the bores. A vial is engaged to a container for liquid communication by snapping the connectors' jaws around their respective inlets, causing the connectors' hollow spikes to pierce their respective plugs. However, not until the container is squeezed is the plug expelled from the blocked bore and communication established between vial and container.