A container cover for use with a container having a neck. The cover includes a lid, a skirt extending downward from the circumference of the lid, and a concentric plug seal extending from the lid inside the skirt. The cover also may include vent holes in the lid. The skirt preferably includes six lock panels. The sides of the lock panels are defined by vertical slots in the skirt, and each lock panel features at least one inwardly-projecting lock. When the cover is locked on the container, the locks engage a lip on the container neck. When a user wishes to remove the cover, the user pulls up on the edge of a lock panel, disengaging the locks from the container lip and removing the cover.