Abstract: A collapsible treatment container has a rectangular elongated base whose outer edge is formed at the rim provided with hinges on which pivot a pair of opposite side walls and another pair of opposite end walls. The side walls and end walls are both centrally formed with stiffening ribs terminating at their bottom in abutments engageable with formations on the base so as to prevent pivoting of these walls beyond an erected position perpendicular to the base, but allowing them to be collapsed and flattened down over the base. The end walls are formed with two spaced sockets and the side walls have tongues of projections engageable with the sockets so as to rigidly lock the assemblies together. The sockets at each corner of the assembly are so arranged and constructed that the tongue or tongues closer to the hinge are engaged in their respective socket or sockets before the other so as to insure easy assembly of the structure.