A holding device (1) for assembling a medical device with a receiving vessel (2) and a holder (3) for a cannula (11), directed towards an open front end (6) of the receiving vessel (2). A flow-through bore of the cannula (11) is connected by a connecting passage (22) between the holder (3) and a front wall (8) of the receiving vessel (2), incorporating a flow passage (21) of a holding part (20) arranged eccentrically with respect to a longitudinal axis (5) of a receiving chamber (9) of the receiving vessel (2). Disposed between the connecting passage (22) and the receiving chamber (9) is an openable hose valve (15). Disposed on the jacket portion (4) of the receiving vessel (2) is a first connecting part (23), whilst a second connecting part (24) is disposed on a support part (14) of the holder (3). A continuous circumferential gas-tight and liquid-proof joint is provided between the holder (3) and the receiving vessel (2).