Abstract: A preformed concrete unitary manhole base section is formed with a polygonal exterior wall with a plurality of substantially flat faces each aligned in a different direction. Some of the faces are formed with cylindrical openings into which standard drain conduit end portions closely fit. Compressible annular seals between the opening walls and the end portions effect a watertight seal between the section and the conduits. Interior flow contours are formed within the section between the openings. Separate plural handling and alignment facilitating means are formed in the exterior wall.