In article ,
Peggie Hall wrote:

Any of the above is possible...the one thing I'm sure of is that the
problem IS the tank vent--that something about it has changed that's
reducing the air flow. Find it and you'll cure the odor problem.

I'm mostly tagging in to thank you for your advice. Backing up your
analysis isn't really needed.

This spring, I plumbed our second vent line a bit better. It's 3/4" ID,
a couple of feet long, and now goes pretty much straight up to a nylon
through-hull high on the hull. The first vent is about 1.25" ID and
only a few inches long, but includes a 90 degree bend. Not an ideal
installation, but the results of the combination are amazing. With just
the single actually active vent, we still had odor when we flushed. Now,
the tank contents are virtually odor free, as we found out when the
toilet backed up. The major smell was a slightly yeasty odor from what I
believe was an overdose of Odorloss (it diminished greatly the second
time a few weeks later), and there's nothing noticable downwind when
someone flushes.

Oxygen, LOTS of oxygen!

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/