Abstract: An upwardly opening outer receptacle is provided having upstanding side wall portions and closed at its lower end by means of a bottom wall. An upwardly opening inner receptacle having upstanding side wall portions and closed at its lower end by means of a bottom wall is supported within the outer receptacle with the bottom wall of the inner receptacle spaced above the bottom wall of the outer receptacle. The outer and inner surfaces of the side wall portions of the inner and outer receptacles define corresponding circumferentially spaced portions disposed in surface-to-surface contact with each other and corresponding circumferentially spaced portions spaced from each other so as to define upstanding passages therebetween communicating with the space between the bottom walls at their lower ends and opening upwardly at their upper ends.