Abstract: A serviceable multiport conversion system for a conventional butterfly valve includes two fittings. A first "T" fitting contains two passageways which join at an internal common bore adjacent a separating wall, the wall defining a secondary seat of the multiport valve. Circumscribing the common bore is an annular flange. A second fitting may be a similar "T" fitting or an "L" fitting. The "L" fitting contains a single passageway which terminates at an internal bore circumscribed an annular flange. In use, the butterfly valve is removably positioned in sealing engagement between two fittings, with the flanges releasably attached and the inner diameters of the flanges co-extensive with the butterfly valve bore. When a butterfly valve is positioned between an "L" fitting and a "T" fitting and the valve is in its closed position, there is no fluid communication between the passageway of the "L" fitting and the passageways of the "T" fitting.