, A connector system providing a releasable, liquid-tight seal for a fluid system, the connector system comprising: a female connector, having a cylindrical opening along a longitudinal axis with an inner circumferential surface; and a male connector, having a tubular end section along the longitudinal axis, which is to be inserted in an insertion direction into the cylindrical opening, wherein inside the tubular end section a fluid passage is formed along the longitudinal axis, and wherein on an outer circumferential surface of the tubular end section, annular protrusions (B, C) are integrally formed, the annular protrusions (B, C) comprising: an intermediate protrusion having an outer diameter (Rb), which is bigger than an inner diameter of the cylindrical opening, and a rear protrusion located with respect to the insertion direction behind the intermediate protrusion having an outer diameter (Rc), which is bigger than the outer diameter (Rb) of the intermediate protrusion; wherein, when the tubular end section with the annular protrusions (B, C) is inserted into the cylindrical opening, the intermediate protrusion and the rear protrusion each form a press-fit with the inner circumferential surface of the cylindrical opening, whereby a liquid-tight seal between the male connector and the female connector is generated, wherein the annular protrusions further comprise an annular front protrusion located with respect to the insertion direction in front of the intermediate protrusion, which has an outer diameter, which is the same or smaller as the inner diameter of the cylindrical opening; wherein a contour of a protrusion (A, B, C) is defined by the shape of its outer surface along the longitudinal axis; and the region of the contour of a protrusion (A, B, C), which is in contact with the female connector in a press-fit, has the same convex shape in insertion and extraction direction along the longitudinal axis, wherein the male connector is made of a single material, and wherein the female connector is made of a single material, which is more elastic than a material of the male connector, wherein no elastomeric component is used in the connection system to generate the liquid-tight seal. a female connector, having a cylindrical opening along a longitudinal axis with an inner circumferential surface; and a male connector, having a tubular end section along the longitudinal axis, which is to be inserted in an insertion direction into the cylindrical opening, wherein inside the tubular end section a fluid passage is formed along the longitudinal axis, and wherein on an outer circumferential surface of the tubular end section, annular protrusions (B, C) are integrally formed, the annular protrusions (B, C) comprising: an intermediate protrusion having an outer diameter (Rb), which is bigger than an inner diameter of the cylindrical opening, and a rear protrusion located with respect to the insertion direction behind the intermediate protrusion having an outer diameter (Rc), which is bigger than the outer diameter (Rb) of the intermediate protrusion; an intermediate protrusion having an outer diameter (Rb), which is bigger than an inner diameter of the cylindrical opening, and a rear protrusion located with respect to the insertion direction behind the intermediate protrusion having an outer diameter (Rc), which is bigger than the outer diameter (Rb) of the intermediate protrusion; wherein, when the tubular end section with the annular protrusions (B, C) is inserted into the cylindrical opening, the intermediate protrusion and the rear protrusion each form a press-fit with the inner circumferential surface of the cylindrical opening, whereby a liquid-tight seal between the male connector and the female connector is generated, wherein the annular protrusions further comprise an annular front protrusion located with respect to the insertion direction in front of the intermediate protrusion, which has an outer diameter, which is the same or smaller as the inner diameter of the cylindrical opening; wherein a contour of a protrusion (A, B, C) is defined by the shape of its outer surface along the longitudinal axis; and the region of the contour of a protrusion (A, B, C), which is in contact with the female connector in a press-fit, has the same convex shape in insertion and extraction direction along the longitudinal axis, wherein the male connector is made of a single material, and wherein the female connector is made of a single material, which is more elastic than a material of the male connector, wherein no elastomeric component is used in the connection system to generate the liquid-tight seal.