A catheter assembly system comprising: a catheter adapter having an inner lumen extending between a proximal opening of the catheter adapter and a distal end of the catheter adapter; a septum disposed within and selectively sealing the inner lumen; a vent channel that fluidly connects the proximal opening and distal end of the catheter adapter by bypassing the septum; a septum activator disposed within the inner lumen proximal to the septum and having a proximal opening, the septum activator being configured to advance distally through a slit in the septum; and an activator attachment comprising: a proximal end having a proximal opening; a connector portion comprising a set of threads; a probe member; and an extension member that extends from the distal end of the probe member, wherein a lumen of the activator attachment extends from the proximal opening of the activator attachment through the probe member and the extension member, characterized in that in response to the activator attachment being inserted into the proximal opening of the catheter adapter to a first position, the probe member inserts into the proximal opening of the catheter adapter and contacts a proximal end of the septum activator, the extension member inserts into the proximal opening of the septum activator, the lumen is in fluid communication with the inner lumen of the catheter adapter, and the slit in the septum is closed, and in response to the connector portion being threaded to the proximal end of the catheter adapter, the activator attachment is distally advanced from the first position to a second position, and the probe member forces the septum activator distally through the septum. a catheter adapter having an inner lumen extending between a proximal opening of the catheter adapter and a distal end of the catheter adapter; a septum disposed within and selectively sealing the inner lumen; a vent channel that fluidly connects the proximal opening and distal end of the catheter adapter by bypassing the septum; a septum activator disposed within the inner lumen proximal to the septum and having a proximal opening, the septum activator being configured to advance distally through a slit in the septum; and an activator attachment comprising: a proximal end having a proximal opening; a connector portion comprising a set of threads; a probe member; and an extension member that extends from the distal end of the probe member, wherein a lumen of the activator attachment extends from the proximal opening of the activator attachment through the probe member and the extension member, a proximal end having a proximal opening; a connector portion comprising a set of threads; a probe member; and an extension member that extends from the distal end of the probe member, wherein a lumen of the activator attachment extends from the proximal opening of the activator attachment through the probe member and the extension member, characterized in that in response to the activator attachment being inserted into the proximal opening of the catheter adapter to a first position, the probe member inserts into the proximal opening of the catheter adapter and contacts a proximal end of the septum activator, the extension member inserts into the proximal opening of the septum activator, the lumen is in fluid communication with the inner lumen of the catheter adapter, and the slit in the septum is closed, and in response to the connector portion being threaded to the proximal end of the catheter adapter, the activator attachment is distally advanced from the first position to a second position, and the probe member forces the septum activator distally through the septum.