system in addition to the filter a regulator and check valve are also provided for enhancing the performance of the delivery system the regulator is used to assure that a constant and uniform air pressure is supplied to the delivery system and the check valve is incorporated to prevent back flows into the filter and air supply system because of the check valve when pressure is relieved from the air supply side already introduced gas and possibly even liquids are prevented from backing up and potentially contaminating the filter and air source in this manner future provision of clean air is further assured contamination resulting from the suck back action is dealt with using a disinfecting sterilizing wash through the delivery system and dental instruments used upon a patient the disinfectant sterilant is not only used to clean the delivery system but it may also be dispensed into the patient 39 s mouth to produce a foaming and sometimes therapeutic action one drawback of the application of the disinfectant into a patient 39 s mouth is its extreme offensive taste to some persons as a result many dental professionals and practitioners are reluctant to use such disinfectants in a patient 39 s mouth in spite of the possible therapeutic benefits for fear that the taste will offend the patient the present invention relieves such apprehension by providing a ready means for quickly and selectively changing the flow to the patient from the possibly distasteful disinfectant.