A catheter assembly 10 comprises a catheter 12 including a longitudinally extending wall 16 with inner and outer surfaces. The inner surface of the wall defines a bore 22 extending longitudinally through the catheter defining a first lumen 52 and a second lumen 54. At least one of the first and second lumens communicates with an opening in the outer surface of the wall at a distal end of the catheter. An elongated separator 14 includes a longitudinally extending surface that at least partially defines the second lumen. The longitudinally extending surface of the separator is disposed asymmetrically relative to the bore when viewed in cross-section taken transverse to the longitudinal extent of the separator adjacent to a distal end of the separator. At least a portion of the separator is movable relative to the bore and the inner surface of the catheter wall.