An anti-reflux syringe assembly having a reservoir for containing a fluid, the reservoir having a cylindrical side wall, an open distal end, and a proximal end having a proximal end wall provided at its axial center with a through opening; a piston slidable in leaktight manner in the reservoir, the piston having a distal end adapted to connect to a plunger passing through the open distal end of the reservoir, and a proximal end having a proximal end wall. The proximal end walls of the reservoir and of the piston are conical, and the proximal end wall of the reservoir forms an angle and the proximal end wall of the piston forming an angle , with 3<<5.

Embodiments of the invention are directed to flush syringe assemblies comprising an integrated contamination-prevention device integrated with device connector flushing positioned so that the practitioner cannot forget to apply disinfectant. The flush syringe assemblies comprise a barrel with an elongate plunger rod disposed therein and a cap comprising a passageway. The plunger rod includes a stopper of which at least a portion can be embedded in the passageway of the cap to form a plug in the cap. Methods of flushing a vascular access device (VAD) while providing a flush syringe assembly described herein are also disclosed.