A system for making blow molded receptacles is disclosed generally comprising two mold portions that, when positioned adjacent each other, at least partially enclose a cavity defined by a molding surface, against which the walls of a blow molded receptacle are blown. One of the portions is a mold core, which has a base surface and a raised portion extending out from the base surface into the cavity. The raised portion has an outer surface and a side surface, which results in a corresponding, inner sidewall on the blow-molded receptacle. The raised portion houses a punch partly disposed in an opening in the side surface for punching a hole in the sidewall. In some embodiments, the side surface is substantially perpendicular to the seal between the two mold portions, and an actuator displaces the punch in a direction substantially parallel to the seam.