Jeff, it's interesting to find a Canadian built piano in Seattle!
(Perhaps I should say a Quebec built piano.)  My first player was
a Willis upright with the Ampico system -- and I did not even know
what "Ampico" meant, but that was 45 years of rebuilding past.

Your question: suction supply for tracker system.  The older system
took the supply from a nipple off the manifold on top of the foot
pumps.  This made the tracker work in both play and rewind which they
decided was not wonderful for the rolls.

Next, the supply was taken from the player stack because the supply
would automatically be shut off during rewind.  Where you found the
patch over the hole was the original location of an elbow to connect
by tubing to the tracker.

This elbow was made tapered with a series of grooves on one end and it
was that end that was pressed into the hole.  It was glued or sealed
into place with either hot glue or burnt shellac.  Those I have seen
are in a hard to reach spot and usually require removal of the top
stack to gain access.

That style of tracker that allows for transposing can be a bit slow so
be sure to keep it well cleaned out and leak free.  Hope this helps.

Regards,
Ken Vinen, Aylmer, Ontario, Canada