Are you saying the stanchion is threaded? Mine has just a tubing nipple- the hose slips over and is clamped over it. A correct size rubber “cork” could be tapped into the tubing to stopper it.
BTW the vents are tube-within-a-tube type. The 1/2” vent tube extends up into the 1” stanchion tube, to just below the lower lifeline hole.
BTW the vents are tube-within-a-tube type. The 1/2” vent tube extends up into the 1” stanchion tube, to just below the lower lifeline hole.