On my 1990 H-33.5, the exhaust hose from the mixing elbow to the Vernalift Water Muffler is 2.000" ID Wet Exhaust. All the ports on the water muffler are 2.000", so the exhaust hose from the water muffler to th exhaust port on the hull is also 2.000" ID Wet Exhaust hose. I also have the Yanmar 2GM20F engine.
