I checked it today, and it's actually a two inch interior diameter standpipe. It's the cap that looks larger. That is the size of the hole in the bottom of the boat. The standpipe cap is above the waterline. It strongly resembles the size of pipe that once took fuel oil in houses in Canada and the U.S. Northeast.
The Venturi unit is here: http://mermaidmarineair.com/marine-d...ndensator.html
It's pretty straightforward, but is it worth 200 bucks? Maybe, or maybe I can whip one up out of barbeque parts and hose cheaper.