A septum is disclosed that can be utilized in a catheter assembly to selectively seal an opening in the catheter assembly. The septum has a tube portion and a plug portion. The plug portion has a slit extending through it. The septum can transition from a non-collapsed state to a collapsed state. When the septum is in a non-collapsed state, the plug portion is offset from the tube portion such that some of the length of the slit extends outward from the distal end of the tube portion. When the septum transitions to the collapsed state, the plug portion is moved inward into the internal cavity such that some of the length of the slit may or may not extend outward from the distal end of the tube portion.