A syringe adaptor (20) includes a body (22), shaped to define a body lumen, a syringe fitting (30) at a proximal end of the body, configured to connect to a distal end of a syringe, a needle (32) extending distally from the syringe fitting into the body lumen, a septum housing (24), and an elastomeric septum (26) mounted inside the septum housing. The septum includes a proximal face (54), shaped to define an aperture (56) having an aperture diameter (d1), and a distal face (58). The septum is shaped to define a cavity (62), joined to the aperture, having a cavity diameter (d2) that is larger than the aperture diameter. The septum housing is configured to slide proximally within the body lumen such that a distal end of the needle contained in the cavity passes through the distal face of the septum. Other embodiments are also described.
