A removable cap assembly includes a cap having a curved side wall having an inner surface and an outer surface. A top portion extends from the curved side wall, a boss extending perpendicularly from the top portion. The boss has a bottom and a top, a first circumferential rib extending perpendicularly from the top of the boss and a second circumferential rib extending perpendicularly from the bottom of the boss. The boss and rib defining an opening in the cap, the opening has a width and a height. A stopper is dimensioned to seal the opening, the stopper has a hole therein configured to allow a fluid to flow therethrough. The stopper is maintained in the cap by the boss and second circumferential rib, the stopper includes a disc shaped base. A cylindrical wall portion extends from the base, a first groove in the base surrounding the wall portion. The first groove is dimensioned to receive the bottom of the boss and a second circumferential groove at a bottom of the wall dimensioned to receive the second circumferential rib.