A manifold assembly useful in patient ventilation/aspiration systems includes as stop cock valve (22) with a hollow stem (26) and a transverse slot (54) arranged to permit the stem (26) to be rotated between open and closed positions. In both positions, a ventilating pathway is maintained through the slot (54) and the stem (26) between ventilator and patient connection ports of the manifold. In open position the stem (26) provides a travel pathway for a catheter between the patient connection port and an access port of the manifold. In closed condition, the stem (26) seals this travel pathway.
