A removable cap assembly having a cap with a curved side wall having an inner surface and an outer surface. A top portion extends from the side wall. A boss extends perpendicularly from the top portion in the shape of an inverted trapezoid, where the boss has a bottom and a top. A first circumferential rib extends perpendicularly from the top of the boss. A stopper is dimensioned to seal the opening, having an inverted trapezoidal shape complementary to the boss. The stopper is maintained in the cap by the inverted trapezoid shape of said boss. The stopper includes a disc shaped base, a cylindrical wall portion extending from the base, a first groove in the base surrounding the wall portion dimensioned to receive the bottom of the boss. An appliance member is adapted to be positioned within the hole and extending through the opening.