Have a 2014 376BHOK & I want to connect the waste drains. I had a neighbor camping last summer tell me he did it when he saw me dragging my sewer hose to the back lines. I was not able to check his out & have searched the forum with no luck.
I think that connecting the gray tanks wouldn't be a problem. I wouldn't connect the two black tanks as I think there would be too much level pipe run between the two would only lead to trouble at some point.