We have that issue. The source of our problem is when we fill the gray tank, it no longer backs up onto the shower, instead it flows under the shower floor and across the floor. In order to fix, the repair place said that they would have to remove the bath to get to it. Since we were no longer under warranty, it is not worth it to fix, we just use an external waste tank.
If you are under warranty, i would get the dealer to look at it.
HTT: "EscapeII" 2016 Shamrock 23WS (current)
PUP: "Escape" 2010 Rockwood HW 277 (gone)
TV: "Bruce" 2011 Dodge Durango V8 Hemi Crew
Just us gals (me, Sis and our daughters)
Traveled 19520 miles and 209 nights in 7 years and counting