A removable cap assembly having a cap, a stopper and a sipper tube. The cap has a curved side wall which has an inner and outer surface. From this wall extends a top portion. A boss extends perpendicularly from the top portion. The boss has a bottom portion and a top portion. A circumferential rib extends perpendicularly from the top portion of the boss. The boss and rib define an opening in the cap. A stopper is provided that is dimensioned to seal the opening of the cap. The stopper is maintained in the cap by the boss and circumferential rib. The stopper includes a disc-shaped base and a cylindrical wall portion that extends therefrom. Additionally, a first groove that is dimensioned to receive the bottom portion of the boss is positioned in the base around the wall portion. Also, a second circumferential groove is positioned in the top portion of the wall portion. This second, groove is dimensioned to receive the rib. The stopper has a hole for receiving a sipper tube.