Abstract: A cover or lid of lightweight relatively flexible material including a circular top having a plurality of first planar segments circumferentially spaced along the circular top. Each first planar segment is connected to an adjoining first planar segment by a plurality of first inclined surfaces defining a plurality of first trapezoidal grooves. A sidewall is integrally formed with and extends downwardly from a peripheral edge of the circular top. The sidewall has a plurality of second planar segments circumferentially spaced along the sidewall with each second planar segment connected to an adjoining second planar segment by a plurality of second inclined surfaces defining a plurality of second trapezoidal grooves. The plurality of first planar segments and first trapezoidal grooves of the circular top are aligned with the plurality of second planar segments and second trapezoidal grooves of the sidewall.