A container includes a containing structure defining an opening and an annular lip radially extending from a distal edge of the opening. A cover is selectively and water-tightly closing the opening. The cover includes a annular rib formed on a bottom thereof and a flange radially extending therefrom wherein the flange abuts against the annular lip when the cover water-tightly closing the opening. A tongue extends from the flange and a pre-broken line is formed on the tongue, wherein the pre-broken line encircles a pre-broken portion and a stopper is formed on a bottom of the pre-broken portion. The tongue forms a griphook for user to easily detach the cover from the containing structure when the pre-broken portion is detached from the tongue along the pre-broken line.