Get the Valve used here https://amzn.to/2ZzLUx9
These are NOT UP TO CODE in more civilized parts of the country and I fully understand why. They save the builder a few bucks when they buy packs of them and they don't have to create a roof stack.. Which is the RIGHT WAY. At first I had some idea what it was but did not fully understand. Oh.. The stink is near 90% better. It will never be 100% by design.