First photo I have put on this forum. Hope you can view it. It shows my sewer outlet configuration. The black and gray tank feed together to a vertical discharge point where the tabs are broken. If you can see the photo, the discharge fitting, which is a Valterra fitting, has the sliding shutoff valves incorporated into it. In my case Dusty R's solution would not have been practical. However,
the link Fubeca provided was a simple fix. My order from Etrailer came quickly and all I had to do was to remove the remaining tabs and glue the new adapter on. It fit perfectly and was simple. Job done. Thanks guys.