Connecting element for connecting at least one flexible tube, wherein - the connecting element comprises a main body, - the main body includes a central portion and at least one mandrel extending away from said central portion, - a duct extends between the mandrels via the central portion or within the mandrel to the central portion, respectively, - the mandrel is insertable into the flexible tube, - wherein a front edge is arranged at an outer end of at least one mandrel, wherein the front edge of at least one mandrel is inclined and/or - wherein at least one mandrel includes at least one sealing edge (26, 28) enclosing circumferentially said mandrel and wherein the at least one sealing edge is inclined, characterized in that - the connecting element comprising at least one ring sleeve, wherein at least one mandrel is enclosed by one ring sleeve and/or wherein the ring sleeve is rotatable relative to the mandrel between an opened state and a closed state, so that a form fit between the flexible tube and the mandrel is obtained in the closed state and/or wherein the mandrel is insertable into the flexible tube, while said flexible tube is enclosable, respectively, by the corresponding ring sleeve, - and that the main body or the ring sleeve includes at least one notch extending along the circumferential direction of the mandrel, wherein at least one cam of the ring sleeve or main body, respectively, is guided or guidable within said notch during the ring sleeve is rotated relative to the mandrel, - whereby the at least one cam and the notch allow a stable, but rotational connection between the main body and the ring sleeve. - the connecting element comprises a main body, - the main body includes a central portion and at least one mandrel extending away from said central portion, - a duct extends between the mandrels via the central portion or within the mandrel to the central portion, respectively, - the mandrel is insertable into the flexible tube, - wherein a front edge is arranged at an outer end of at least one mandrel, wherein the front edge of at least one mandrel is inclined and/or - wherein at least one mandrel includes at least one sealing edge (26, 28) enclosing circumferentially said mandrel and wherein the at least one sealing edge is inclined, - the connecting element comprising at least one ring sleeve, wherein at least one mandrel is enclosed by one ring sleeve and/or wherein the ring sleeve is rotatable relative to the mandrel between an opened state and a closed state, so that a form fit between the flexible tube and the mandrel is obtained in the closed state and/or wherein the mandrel is insertable into the flexible tube, while said flexible tube is enclosable, respectively, by the corresponding ring sleeve, - and that the main body or the ring sleeve includes at least one notch extending along the circumferential direction of the mandrel, wherein at least one cam of the ring sleeve or main body, respectively, is guided or guidable within said notch during the ring sleeve is rotated relative to the mandrel, - whereby the at least one cam and the notch allow a stable, but rotational connection between the main body and the ring sleeve.