Can I guess that you are interested in this product because you have an issue with odor, perhaps from the bathroom? I have encountered some issues with a sewer smell on occasion. My take is that it occurs after a day of travelling and in my case comes from the shower drain. The solution I have found is to pour some water down the shower drain after stopping. If there is a p-trap below the shower this fills it up again and it forces you to check the tightness of the drain plug for the shower, a second cause of odor.
No, it was never serious enough that I considered a vent extension. And mine would be gray water exhaust. Or are both the gray and black water vented into the same stack?
Paul and Janet Braun
2003 Toyota 4Runner V8 now 2012 Toyota Sequoia V8
Escape 19' 2010 now 2014 Escape 21'