A respiratory face mask (10) is provided suitably sized and configured to engage at least the nose portion and mouth portion of a patient&rsquo；s face. Gas from a gas supply and scavenging set normally used in dentistry is operatively coupled to the mask via a breathing circuit (90) to supply fresh gas and evacuate exhaled waste gas, comrpising a single length of co-axial flexible tubing (136) connected between the face mask and a branched coupling (140). The branched coupling, in turn, includes a first branch for connection to the fresh gas supply nozzle of the &ldquo；dental&rdquo； set-up and a second branch for connection to a flexible flow-through reservoir bag (132, 176) used to store waste or exhaled gas. A one-way valve (172) is disposed between the second branch output nozzle and the input of the flexible bag. The output of the flexible flow-through bag is connected to the vacuum module of the &ldquo；dental&rdquo； set-up. The second branch of the coupling, the one-way valve, and the flexible flow-through reservoir bag define the exhalation limb of the breathing circuit.
