A block-out tube for use in joining together pre-cast concrete members, the block-out tube having an ovalized cross-section, an integral elongate imperforate hollow tubular body with smoothly curved corrugated walls, a rounded tip closing the bottom end thereof, a mounting flange with tear-away nail tabs at the top open end thereof, and a removable transparent member for sealing the top end for preventing water and debris from entering the interior of the tube. The block-out tube, secured by attaching the tear-away tabs to a concrete pouring form, is cast into the top of the lower concrete member, the ovalized corrugated body being embedded therein and the top sealed end being exposed at the top surface thereof, after the removal of the form. When the concrete members are erected and joined, the transparent sealing means at the top end is removed, the block-out tube is filled with grout, and a structural rod extending outwardly from one member is fitted into the grout-filled tube as the one member is joined to the other member, the grout engaging the structural rod and the corrugated tube wall, forming a strong joint between the two concrete members.