To provide an access route which is leaktight and at the same time permits mobility and exact positioning of an instillation catheter (6), an arrangement comprising an instillation catheter (6) and a connector piece (1) for attachment to a tracheal or endotracheal tube is proposed. The connector piece (1) has a distal end (1a) for attachment to the tube, and a proximal end (1b) for attachment to a ventilation and/or suction device and comprises a branch (5) which serves for insertion of the catheter (6) and in which a valve (2) is arranged. The valve (2) is made, at least in some areas, from an elastically deformable material and can be opened by insertion of the catheter (6). The valve further comprises a proximal through-opening (21) whose inner wall has a means allowing sealing against axial flow of fluid between catheter (6) and inner wall, and, in the distal direction from the through-opening, it has a beak section (22) which, at its beak tip (23), has a normally closed slit (24).
