Abstract: The present invention is a cavity for hybrid waterbeds. The side walls of the cavity are of resilient grade foam and are broader at the top plane than at the bottom plane. The hybrid waterbed cavity of the present invention retains the positive qualities found in conventional waterbed cavities of holding and retaining a waterbed mattress, and eliminates the undesirable qualities of the reduction of sleeping surface area and the creation of excess stress on the surrounding cover which occurs when conventional cavities are subjected to body weight.

Abstract: A waterbed mattress system including wave dampening filler material is described which can be rapidly drained of the liquid contained therein. The invented system is provided with at least one perforated pipe which channels the liquid to the drain port. The perforated pipe and method for using the same are also described.