Picture of the 2 hole grommet is up above in a previous post. Your summary sounds correct. Mine is vacuum activated at the water valve. Also mine is non A/C. Don't have a water valve yet but will have one soon. Would really appreciate a photo but what you have suggested helps.

Question though: if the hole is a little to the right and below the blower motor, wouldn't that be the original hole location for the Air Grabber vacuum lines going to the vac canister as well? Would there be 2 holes in that location side by side for Strato Vent cars with Air Grabber in that case?