A flush syringe assembly comprising: a barrel including a side wall having an inside surface defining a chamber for retaining fluid, an outside surface, an open proximal end, a distal end including a distal wall with a tip extending distally therefrom having a passageway therethrough in fluid communication with the chamber, the barrel further comprising an outside surface containing one or more annular positioning discontinuities (167, 168); a cap comprising a distal end and a proximal end defining a length, an irregularly shaped outer wall, a profiled center passageway providing fluid communication from the chamber to a patient's vascular access device, further comprising a distal end annular channel that releasably attaches the cap to the VAD, and a proximal end annular channel that releasably attaches the cap to the barrel; a releasable disinfecting system comprising a disinfectant; an elongate plunger rod disposed within the barrel, the plunger rod comprising a distal portion and a proximal portion, the plunger rod further comprising a distal end including a stopper slidably positioned in fluid-tight contact with the inside surface of the barrel for expelling fluid from the chamber by movement of the stopper relative to the barrel, the stopper having a distal face and a proximal end, the distal face of the stopper further comprising a profiled stopper tip that is detachable from the stopper and seatable in the cap when the plunger rod is fully depressed; a sleeve external to the barrel having an inside surface and an outside surface, an open proximal end containing at least one flange, and an open distal end defining a recess with an irregular inner surface to contain and prevent rotation of the cap relative to the sleeve, the distal end further connected to the releasable disinfecting system, the inside surface of the sleeve further comprising one or more annular positioning discontinuities complementary to the one or more annular discontinuities (167, 168) on the barrel which together control distal motion of the barrel relative to the sleeve; and a quantity of flush solution in the chamber between the stopper and distal wall of the barrel. a releasable disinfecting system comprising a disinfectant; an elongate plunger rod disposed within the barrel, the plunger rod comprising a distal portion and a proximal portion, the plunger rod further comprising a distal end including a stopper slidably positioned in fluid-tight contact with the inside surface of the barrel for expelling fluid from the chamber by movement of the stopper relative to the barrel, the stopper having a distal face and a proximal end, the distal face of the stopper further comprising a profiled stopper tip that is detachable from the stopper and seatable in the cap when the plunger rod is fully depressed; a sleeve external to the barrel having an inside surface and an outside surface, an open proximal end containing at least one flange, and an open distal end defining a recess with an irregular inner surface to contain and prevent rotation of the cap relative to the sleeve, the distal end further connected to the releasable disinfecting system, the inside surface of the sleeve further comprising one or more annular positioning discontinuities complementary to the one or more annular discontinuities (167, 168) on the barrel which together control distal motion of the barrel relative to the sleeve; and a quantity of flush solution in the chamber between the stopper and distal wall of the barrel.