A conduit-coupling adaptor configured for mutually joining conduits of disparate diameters includes a central conduit with interior and exterior surfaces extending longitudinally between central-conduit first and second ends. The central-conduit first and second ends define, respectively, first-end and second-end coupling sleeves that extend longitudinally in opposite directions and terminate at, respectively, first and second openings. The coupling sleeves can be implemented, alternatively, as male or female coupling members relative to other conduits. A first-end skirt includes a skirt wall concentrically disposed about at least a lengthwise portion of the central-conduit first end. The skirt wall has skirt-wall inside and outside surfaces that longitudinally co-extend with at least a portion of the first-end coupling sleeve and are joined to the central-conduit wall by a shoulder. The skirt-wall inside surface defines a socket that is configured as a female connector for insertably receiving a male coupling member of another conduit.