Steel Cradle Tanks See list below.Cradle Tanks can be selected for stationary or transportable (non-D.O.T. regulated) applications both indoors and outdoors. The elliptical tank lowers the center of gravity to enhance stability and visibility. The tanks feature a standard collection sump on the bottom for full drain out. These tanks require the bottom to be fully supported with a cradle for use. The tanks are manufactured from medium-density polyethylene with U.V. inhibitors. Tank walls are translucent for level viewing and equipped with gallon indicators.