interior 40 of the barrel 22 on the opposite side of the plunger seal 54 from the variable volume fluid chamber 62 the valve assembly 20 is a housing for an aspiration valve 66 and a disposal valve 68 the valve assembly 20 is preferably fabricated from a disposable material such as a rigid plastic and has an integral construction or is assembled from a plurality of separate components the aspiration valve 66 is positioned in an aspiration valve chamber 70 having an aspiration inlet opening 72 and an aspiration outlet opening 74 the disposal valve 68 is correspondingly positioned in a disposal valve chamber 76 having a disposal outlet opening 78 the aspiration and disposal valve chambers 70 76 share a common disposal opening 80 which is positioned between the aspiration valve chamber 70 and the disposal valve chamber 76 and provides fluid communication therebetween the aspiration inlet opening 72 is positioned adjacent to the aspiration intake coupler 30 b and provides fluid communication between the continuous fluid passageway of the aspiration intake 18 and the aspiration valve chamber 70 via the back end 28 of the aspiration intake 18 and the continuous fluid passageways of the aspiration intake couplers 30 a 30 b the aspiration outlet opening 74 is positioned adjacent to the barrel coupler 46 b and provides fluid communication between the aspiration valve chamber 70 and the variable volume fluid chamber 62 via the.