Abstract: Apertures in the cast concrete walls of a swimming pool are lined with tubular inserts entirely received in the apertures in sealing, conforming engagement with the concrete. The length of each insert in the direction of wall thickness is equal to or shorter than the corresponding length of the receiving aperture. The insert essentially consists of a solid mixture of a particulate, rigid, inorganic material, such as quartz sand, and a smaller amount of a more resilient, synthetic organic resin binder. A fastening flange is provided in the bore of the insert for fastening the insert in a form while the wall is being built by pouring fluid concrete mixture into the form. The flange provides a fastening base for later installed fittings, pumps, etc. During construction of the swimming pool, a form bounding a cavity is erected.