A box culvert and gasket assembly is provided that enables fluid-tight bell-and spigot joints to be formed between abutting ends of box culverts. The joints according to the assembly of the present invention can remain fluid-tight up to at least 13 psi of water pressure. The gasket is preferably a one-piece, endless rubber gasket that is applied over the end of a spigot that is rectangular in end elevation. The corners of the rectangular spigot are rounded to enable the gasket to extend continuously over the corner without the need for 45.degree. cuts and splices. Preferably, the gasket is made from a single elongate gasket piece that is cut to size and that has ends that are bonded together via a butt vulcanization technique. A storm drain and sewer assembly and a method of forming a fluid-tight bell-and spigot joint are also provided.