Apparatus, systems and methods for flushing a lumen of a catheter instrument to reduce or eliminate bubbles within the lumen. An interface valve is adapted for attachment to a proximal end of the catheter instrument and can receive a working instrument for insertion into the catheter instrument lumen. A fluid supply line and purge lines are coupled to the interface valve and in fluid communication with at least a portion of the interface valve lumen. Flow of fluid (e.g. saline and a gas such as bubbles) through purge lines is controllable using clamps such that fluid flowing into the interface valve lumen can be manipulated to flow in different directions through different portions of the interface valve lumen for evacuation through different purge lines, thus allowing for purging of forward and backward flows to remove gas or bubbles from the catheter instrument lumen.