Cartridge to dispense a product in a container

A cartridge which cooperates with a neck of a container to allow a product contained in the cartridge to flow into said container, said cartridge comprising:

• a reservoir containing the product, said reservoir having a lower opening and a lower wall;
• a moveable sealer comprising a cylindrical body and a flap closing the lower opening of the reservoir, wherein said cylindrical body is dimensioned to surround the lower wall of the reservoir and to slide along said lower wall to define a closed position and an opening position of the reservoir, wherein in the opening position the flap is opened by pressure exerted by the lower wall of the reservoir on said flap;
• and
• a socket surrounding both the lower wall of the reservoir and the movable sealer, said socket comprising an internal relief;
• wherein the moveable sealer further comprises two rings distributed along the cylindrical body, wherein the two rings comprise a lower ring and an upper ring, said lower ring configured to cooperate with the neck of the container, wherein the neck contacts and exerts pressure on said lower ring to slide the cylindrical body along the lower wall of the reservoir to open the flap, and the upper ring comprising holding lugs configured to cooperate with the internal relief of the socket in order to maintain the moveable sealer inside the socket.