Peggy, Just got done reading your reference library article about Holding Tank Odor-Cause and Cure. I bought SeaLand hose earlier this winter per your recomendation and am now planning the system installation. My question has to do with the vent lines. The factory installed lines on my O272 are definitely too small, just as you describe in the article, and the vent line is also much too high where it exits the hull. I have bought one 11/2" thru hull and am now contemplating buying another to make the cross-ventilation set-up you describe in the article. My problem is similar to one I read in a recent post to you. If I run the vent lines slightly above horizontal, they will exit the boat less than 12" above the waterline. It is conceiveable that one of the thru hulls could be underwater when the boat is heeling. What is your suggestion? Problem two is really a question. How far apart (minimum distance) can the twin vent outlets be installed on the tank? I am working with limited space and can't install them fore and aft on the top of the tank without tearing the v-berth apart. The tank is app. 12" wide. Will the vent system work optimally if I install the vent outlets side-by-side toward the rear on the top of the tank? I hope I'm not making a mountain out of a molehill, but as you have often said, "better to ask beforehand and have no regrets". Did you really say that? ;-)
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I really said that 
A single 1.5" vent line should work up to 4' long if it doesn't rise sharper than 45 degrees. Just a foot above the waterline is waaaay to low on a sailboat...so make it longer--if you have to do some surgery on the v-berth to do it right, so be it. It would have been easier if the builder had gotten it right the first time, but he didn't...now it's up to you to either do it right or continue to live with problems. Fortunately your tank is under the v-berth...Go forward with the vent line at least far enough to keep the thru-hullout of the water at maximum heel...and enough to come out the hull about 18" below the toe rail. If that means a gradual (VERY gradual!) bend of no more 15-20 degrees, it still should work. Email me if you still need help.
A single 1.5" vent line should work up to 4' long if it doesn't rise sharper than 45 degrees. Just a foot above the waterline is waaaay to low on a sailboat...so make it longer--if you have to do some surgery on the v-berth to do it right, so be it. It would have been easier if the builder had gotten it right the first time, but he didn't...now it's up to you to either do it right or continue to live with problems. Fortunately your tank is under the v-berth...Go forward with the vent line at least far enough to keep the thru-hullout of the water at maximum heel...and enough to come out the hull about 18" below the toe rail. If that means a gradual (VERY gradual!) bend of no more 15-20 degrees, it still should work. Email me if you still need help.
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