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 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 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 . <EOS>