A catheter assembly includes a cap and a spring-biased tethering member coupled thereto. The cap includes first and second portions, and a transition zone extending therebetween. A girth of the first portion is sized to fit within a distal-most opening of the catheter assembly; and a girth of the second portion tapers from a first size at the transition zone, which is too large to fit within the distal-most opening, to a smaller size at a distal end of the cap. The spring-biased tethering member holds the cap in open and closed positions, when the cap first portion extends within the distal-most opening, and when the cap is separated from the distal-most opening, respectively. At the closed position, the first portion is approximately concentric with the distal-most opening, and at the open position, an entirety of the cap is laterally offset from the distal-most opening.