I always wondered how much reversion is pulled in up the "ramp" versus as moisture molecules in the exhaust gasses. I cant imagine that dam helps too much.

Well, maybe OP will buy some 4" clear vinyl hose and do a test. Add a little food coloring and that would be pretty damn cool to see, IMO

Great service bulletin from Mercruiser to read on this subject:

http://www.boatfix.com/merc/Bullet/01/01_13.pdf

Shut seacocks off. Sorry I had to.

Got your pm. What I did was cut both riser pipes off the same length and cnc'd 4" od / 3.5" id 316ss rings out of 11ga and tigged them. I'd welded 3/4" pipe thread 316ss bungs on the top approximately 3" from the end. My tails are basically the same. 3.5"ss tube /4"ss tube with rings on both ends. Only difference is the exit side I cut 1.25" of the circumference out for the water to escape. If I left the end 100% open I feared the water would drain faster than it would fill and not cool the pipe equally. And I used ss exhaust band clamps to connect the pipes. been running this set up for going on 3 years now and love it