Re: "Flushing question"
The port is there so that you don't have to run it, it backflushes the engine. If you run the hose through it while it's not running you will see the water eventually come out of the prop once it makes it's way down there, this will even work with the engine tilted up at the dock.
It is really for people who keep their boat in the water, so that they can back flush the powerhead at the dock. But it works fine at home on the trailer too.
It is not advised to run the engine while using this backflushing port for the exact reason mentioned, the water pump is not sufficiently lubricated with enough water. If you are only idling, then you may get away with it, but if you plan on running it any higher than idle you will hurt your water pump. A pair of ear muffs cost $5, so if your gonna run it anyway at home, you might as well use the muffs so you know your pump is being lubricated. Why risk it, if you do end up damaging your impeller, you probably won't know it until your out on the water at 5K RPM and a piece breaks off and goes up into your powerhead, so it's not worth it to not run on the muffs.
This is what is wideley known and accepted, and it is what I have heard since the backflushing ports started being put on, I think in '98 or '99. I actually had a friend destroy his impeller pretty quick by not listening to me on this.
That being said, I was watching a video presentation of the E-tec at the NY Boat Show this year, and they had engines running on the backflusher in the video, I was completely confused. I was gonna ask one of the reps there about it, but didn't get the chance.
In any case, you can't go wrong on the muffs. Seeing as how you said you did your own pump or at least impeller, you have seen first hand how tight the fit is inside the housing, so you can see how it wouldn't take much to do impeller damage with lack of water.
On a side note, your better off replacing the whole pump assembly rather than just the impeller, it only costs a little bit more, and I have never seen an assembly come off that didin't have even some minor scoring on the cup or plate. Any scoring lessens the seal the impeller has to push water, therefore lessening the pressure up to the powerhead.
