A seal covering a discharge port of a container is opened without leaving superfluous elements on the container by a container closure unit which has seal-piercing knife-like elements mounted on a flexible dome-shaped base which is located to place the knife-like elements adjacent to the seal. The dome-shaped base is flexed to move the knife-like elements through the seal and then to move them outwardly toward the periphery of the seal to cut slits in the seal. The slits act as fluid passages to permit decanting of the fluid from the container. Once the seal has been opened, the dome-shaped base is removed using a pull ring and discarded. The container closure unit has a cap which is used to close the container discharge port between uses.