JohnR- I don't know how we didn't either, and I won't be surprised if there is some unseen damage that rears it's head in the first few hours of operation.
The water was backed up all the way to the exhaust/water mixing elbow. Also, when I removed the siphon i heard some gurgling and a slight vacuum sound. The through hull valve for the anti-siphon hose was plug tight enough to not allow me to blow air through it and took some heavy wire to punch through the larvae.
I was there for the haul out and relaunch. Nothing out of the ordinary there.
The engineers at Yanmar and Mack Boring have my pictures, observations and have worked very closely with my mechanic. They haven't decided yet whether I had one or two problems. But they are still working on it.
I would also like to let you all know how impressed I have been with Bob at Mack Boring (Yanmar Reps in Chicago). He has promptly responded to every question and took it upon himself to follow up directly with my mechanic and with Yanmar. I promise you that you do not get to see this kind of service very often.