Also, some showers simply drain slow because of the configuration. My Jamboree's shower has always had a slow draining shower. I tried the Zip-it type thing a few times, but it never resulted in any change. Recently, I had a panel removed (for a different issue) that allowed me to see the plumbing configuration under the shower pan, and realized that I've never had a clog issue, it is simply the way the plumbing is configured that forces a slow drainage. Since the shower pan is low, and the holding tank is only slightly below floor level, once you squeeze in a p-trap and the horizontal line to get to the tank, there is no possible way to get it to flow fast.
And yes, grey water backing up into the shower is the classic definition of a full grey tank!
My Jamboree has ONLY the toilet plumbed to the black tank, but my new Itasca class A has the bathroom sink also plumbed to the black tank.
