Abstract: A technique for the rotational molding of hollow articles having separate but structurally integral compartments is described. A mold in which the article is to be formed is provided with a cover between the mold cavities in which the article compartments are to be rotationally molded. The cover is selectively spaced from the mold wall so that a thermoplastic resin used to form the article can pass through the space between the cover and the mold wall to form the article walls for the compartments. The cover spacing from the mold wall is so selected that the build-up of the article's wall eventually seals off this spacing and enables further rotational molding of an article wall over the cover to isolate the compartments. In the specific embodiment, a technique for the rotational molding of a tank with legs below a bottom wall and a continuous uninterrupted interior bottom surface is described.