If you have good water flow from the hose, then it has to be that fitting. if its not then you may have to take it to honda so they can thoroughly flush the cooling system.
I took it in and they said that hornets were making a nest inside. They said it was quite common in ski jets and outboard motors. I am surprised you didn't think of that. I looked at your other answers and you seem to know what you are talking about. I guess this one is what you will get paid for even though I already did that. Kind of lame answer about checking to see if water is coming out of the hose, but there you go.