This shows where the exhaust tube attaches to the exhaust riser. This is where the exhaust gases come out. The cut out near the top is where the water flows out .. so the actual mixing of exhaust gases and water happens in the exhaust tube to cool it down. If you look closely down in the center of the exhaust port you can see corrosion way in the back. A Very Bad Thing(tm). Again I was really close to a catastrophic failure. Moral - buy good exhaust risers and manifolds.