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.