Connection system for releasably force-fittingly coupling a first body to a fluid-carrying system via a fluid-tight membrane , wherein the connection system comprises the membrane and a second body with an interior space which is coupled to the fluid-carrying system, and wherein the first body comprises a first end with a flange , wherein the second body comprises a second end with an interior space , a circumferential wall and an opening , wherein the circumferential wall comprises a membrane contact portion which extends around the opening and which is in contact with the membrane , characterized in that (a) the connection system comprises a disk-shaped holding member with a passage , a first side, a second side and a peripheral outer edge , wherein the first side and/or the passage of the holding member is/are coupled to the membrane , and wherein the second side of the holding member is designed for surface-to-surface contact with the flange of the first body , or (b) the second end of the second body defines a flange-like, disk-shaped holding member having a peripheral outer edge , wherein the flange-like, disk-shaped holding member is in contact with the membrane and is designed for surface-to-surface contact with the flange of the first body , and wherein the first body is fluid-carrying, and wherein the connection system in (a) and (b) further comprises a releasable connection member which is designed to at least partially engage around the peripheral outer edge of the holding member and the flange of the first body , such that the holding member can be releasably force-fittingly fixed to the first body by means of the connection member . wherein the connection system comprises the membrane and a second body with an interior space which is coupled to the fluid-carrying system, and wherein the first body comprises a first end with a flange , wherein the second body comprises a second end with an interior space , a circumferential wall and an opening , wherein the circumferential wall comprises a membrane contact portion which extends around the opening and which is in contact with the membrane , characterized in that (a) the connection system comprises a disk-shaped holding member with a passage , a first side, a second side and a peripheral outer edge , wherein the first side and/or the passage of the holding member is/are coupled to the membrane , and wherein the second side of the holding member is designed for surface-to-surface contact with the flange of the first body , or (b) the second end of the second body defines a flange-like, disk-shaped holding member having a peripheral outer edge , wherein the flange-like, disk-shaped holding member is in contact with the membrane and is designed for surface-to-surface contact with the flange of the first body , and wherein the first body is fluid-carrying, and (a) the connection system comprises a disk-shaped holding member with a passage , a first side, a second side and a peripheral outer edge , wherein the first side and/or the passage of the holding member is/are coupled to the membrane , and wherein the second side of the holding member is designed for surface-to-surface contact with the flange of the first body , or (b) the second end of the second body defines a flange-like, disk-shaped holding member having a peripheral outer edge , wherein the flange-like, disk-shaped holding member is in contact with the membrane and is designed for surface-to-surface contact with the flange of the first body , and wherein the first body is fluid-carrying, and wherein the connection system in (a) and (b) further comprises a releasable connection member which is designed to at least partially engage around the peripheral outer edge of the holding member and the flange of the first body , such that the holding member can be releasably force-fittingly fixed to the first body by means of the connection member . <EOS>