Lift the retaining C clip with an x-acto knife and pull it out.

The nylon part will pull out and reveal a metal end.  Remove the O-ring from it and save for later.

Firmly grab the metal striker for the solenoid, and twist/pull it out.  

With a 1/16th drill bit, drill straight through the metal striker you just removed center to center.

Also drill a vent hole between the terminals to match.

Remove the actuator, return spring, and the small fiber washer from the nylon cylinder.  Carefully expand one loop of the spring so it isn't tempted to go into the hole you just drilled.  

Replace the fiber washer with the O-ring you saved earlier in between the striker and actuator pin.

Previously the O-ring was just used for noise suppression.  Now it will seal port number 3.

Put it all back together.  If you will be applying pressure to port 3, epoxy a hose bib to the outside.