A vessel intended to contain a fluid, of the baby bottle, bottle, flask or tank for a gas or a liquid type, the vessel comprising a container delimiting an internal volume formed from a flexible material and capped with a tubular sleeve, one proximal end of which delimits a housing in combination with the container, and one distal end of which delimits an upper opening allowing the flow of the fluid towards or from the internal volume and including an upper shoulder protruding radially towards the outside of the sleeve, a removable closure device formed from a flexible material, and including a lower shoulder likely to collaborate with the upper shoulder of the sleeve so that a seal is created when the lower shoulder and the upper shoulder are compressed against each other, a coupling system allowing hold and mutual compression of the lower shoulder of the removable closure device and of the upper shoulder of the sleeve, and consisting of the following two parts, independent of each other and both formed from a rigid material: - a first annular ring delimiting a first thread and a flange likely to be inserted into the housing by elastic deformation of the proximal end of the sleeve, the first annular ring being urged to be positioned around the sleeve, under the upper shoulder, by elastic deformation of the upper shoulder, - a second annular ring delimiting a second thread engaging with the first thread by screwing the second annular ring relative to the first annular ring, so that the lower shoulder of the removable closure device and the upper shoulder of the sleeve are likely to be enclosed and mutually compressed between the first annular ring and the second annular ring by the screwing action of the second annular ring on the first annular ring, characterized in that the container delimits an external shoulder, the free face of which is generally orthogonal to the longitudinal extension direction of the tubular sleeve, and that the second annular ring delimits a primary shoulder so that the primary shoulder of the second annular ring bears against the external shoulder of the container when the second annular ring encloses the lower shoulder of the removable closure device and the upper shoulder of the sleeve in cooperation with the first annular ring. a container delimiting an internal volume formed from a flexible material and capped with a tubular sleeve, one proximal end of which delimits a housing in combination with the container, and one distal end of which delimits an upper opening allowing the flow of the fluid towards or from the internal volume and including an upper shoulder protruding radially towards the outside of the sleeve, a removable closure device formed from a flexible material, and including a lower shoulder likely to collaborate with the upper shoulder of the sleeve so that a seal is created when the lower shoulder and the upper shoulder are compressed against each other, a coupling system allowing hold and mutual compression of the lower shoulder of the removable closure device and of the upper shoulder of the sleeve, and consisting of the following two parts, independent of each other and both formed from a rigid material: - a first annular ring delimiting a first thread and a flange likely to be inserted into the housing by elastic deformation of the proximal end of the sleeve, the first annular ring being urged to be positioned around the sleeve, under the upper shoulder, by elastic deformation of the upper shoulder, - a second annular ring delimiting a second thread engaging with the first thread by screwing the second annular ring relative to the first annular ring, so that the lower shoulder of the removable closure device and the upper shoulder of the sleeve are likely to be enclosed and mutually compressed between the first annular ring and the second annular ring by the screwing action of the second annular ring on the first annular ring, - a first annular ring delimiting a first thread and a flange likely to be inserted into the housing by elastic deformation of the proximal end of the sleeve, the first annular ring being urged to be positioned around the sleeve, under the upper shoulder, by elastic deformation of the upper shoulder, - a second annular ring delimiting a second thread engaging with the first thread by screwing the second annular ring relative to the first annular ring, so that the lower shoulder of the removable closure device and the upper shoulder of the sleeve are likely to be enclosed and mutually compressed between the first annular ring and the second annular ring by the screwing action of the second annular ring on the first annular ring, characterized in that the container delimits an external shoulder, the free face of which is generally orthogonal to the longitudinal extension direction of the tubular sleeve, and that the second annular ring delimits a primary shoulder so that the primary shoulder of the second annular ring bears against the external shoulder of the container when the second annular ring encloses the lower shoulder of the removable closure device and the upper shoulder of the sleeve in cooperation with the first annular ring.