stabilize it in place the upper end of the body will be placed where when the lid is attached the upper surface of the lid will be at grade the peripheral wall 32 of the body is a quadrilateral frustum sloping upwardly from the bottom end if preferred the bottom end could be the larger end but structural consideration will prefer the illustrated shape over the reverse or from a prismatic shape which could also be used circular vaults are also in this scope of this invention but quadrilaterals are generally preferred the illustrated shape is well suited to manufacture by injection molding processes which is an advantage in the reduction of cost it is also amenable to rotational molding the lower end includes an upwardly extending peripheral skirt 33 attention is called to buttresses 34 which are integral with or attached to the inside of the skirt and the outside of the peripheral wall these provide strong support for the skirt which in turn provides significant rigidity to the lower end so that side forces are less likely to distort the shape of the body a rim 40 is formed at the top end of the body where a seat 41 is formed by a re entrant wall 42 that terminates in an inwardly extending flange 43 a lip 44 is formed as an inward extension from flange.