An adapter is suitable to be mounted on and to cooperate with the neck of a container in order to allow a product contained in the adapter to flow out into the interior of said container. The adaptor comprises at least one tank which is suitable to contain said product, said tank having a first opening which is suitable to transfer said product from the tank into the interior of the container. Further, the adaptor comprises a single-use or reversible movable means for sealingly closing the first opening. Moreover, the adaptor comprises a means for activating the movable means for sealingly closing so as to allow said movable means for sealingly closing to open and said product contained in the tank to flow out into the interior of the container.
