Gil,

There is no hose connected to that port. About half of of the 10 valves on this manifold have two solenoids and half have only one solenoid and the open port which I assume may be the vent. Unfortunately, I am here by myself so I can't push the button to activate the solenoid and be at the manifold at the same time. I'm going to try to disconnect the lines tomorrow as you suggested and check to see if the piston is bad.