A tubular plug-in type connection sleeve for forming a lead-through of a water pipe with a protective tube thereon through a hole in a wall of a manifold cabinet , the connection sleeve comprising: - a flange portion made of an elastomer, defining, on the outer surface of the connection sleeve, an annular sealing surface ; - a radially outwards extending snapping protrusion on the outer surface of the connection sleeve defining, together with the annular sealing surface, a snapping gap for receiving, when in use, a cabinet wall edge surrounding the hole in the cabinet wall, whereby the annular sealing surface is pressed against the cabinet wall, wherein the snapping protrusion comprises a stop surface extending in a cross-sectional plane of the connection sleeve perpendicular to the longitudinal direction of the connection sleeve, the stop surface facing towards the annular sealing surface ; the annular sealing surface comprising a conical annular section narrowing the snapping gap radially outwards for ensuring a waterproof contact between the annular sealing surface and the cabinet wall snapped, when in use, in the snapping gap; - a tube section made of an elastomer for receiving the protective tube, the tube section inner surface being shaped and dimensioned so as to be set, when in use, against the protective tube received in the tube section; - a gripping protrusion extending radially inwards from the inner surface of the connection sleeve for gripping the protective tube received, when in use, in the connection sleeve; and - a stiffening member made of a plastic material, comprising a closed ring portion extending around the circumference of the connection sleeve, the closed ring portion being coupled to the gripping protrusion for constraining the radially outward retraction of the gripping protrusion, the stiffening member being formed as an integral part of the connection sleeve, the rest of which is made of an elastomer, so as to form a single two-material connection sleeve body. - a flange portion made of an elastomer, defining, on the outer surface of the connection sleeve, an annular sealing surface ; - a radially outwards extending snapping protrusion on the outer surface of the connection sleeve defining, together with the annular sealing surface, a snapping gap for receiving, when in use, a cabinet wall edge surrounding the hole in the cabinet wall, whereby the annular sealing surface is pressed against the cabinet wall, wherein the snapping protrusion comprises a stop surface extending in a cross-sectional plane of the connection sleeve perpendicular to the longitudinal direction of the connection sleeve, the stop surface facing towards the annular sealing surface ; the annular sealing surface comprising a conical annular section narrowing the snapping gap radially outwards for ensuring a waterproof contact between the annular sealing surface and the cabinet wall snapped, when in use, in the snapping gap; - a tube section made of an elastomer for receiving the protective tube, the tube section inner surface being shaped and dimensioned so as to be set, when in use, against the protective tube received in the tube section; - a gripping protrusion extending radially inwards from the inner surface of the connection sleeve for gripping the protective tube received, when in use, in the connection sleeve; and - a stiffening member made of a plastic material, comprising a closed ring portion extending around the circumference of the connection sleeve, the closed ring portion being coupled to the gripping protrusion for constraining the radially outward retraction of the gripping protrusion, the stiffening member being formed as an integral part of the connection sleeve, the rest of which is made of an elastomer, so as to form a single two-material connection sleeve body. <EOS>