A method for forming a closed-ended catheter (20), the method comprising: forming an elongate catheter tube (22) including an outer wall (42) that defines at least one lumen (43), the catheter tube including a distal segment (34)； defining a slit valve (36) through the outer wall of the distal segment； and including a compliant segment (40) in the outer wall of the distal segment, the compliant segment including a durometer below that of surrounding portions of the outer wall, the compliant segment positioned relative to the slit valve such that the compliant segment preferentially deforms when an aspiration force is present in the at least one lumen to assist in opening the slit valve.
