[mtlakejim]

Yes there is a cheap plastic check in that connection. If you have pass thru in front of that compartment it is easy to access back of panel and remove wing fitting off back followed by taping the check out with a screwdriver. Doing so significantly increases flush volume!!

You can eliminate the backflow valve too. Especially if you add hose with ball valve to the outside hose fitting (IE: the same fitting mentioned above). In fact doing so and using clear hose allows me to use my 12volt on board water pump to rinse black tank via the outside shower connection!! Very handy when a good rinse line is not available at dump station!

If access under the bathroom isn’t too hard you might consider cutting the line below the floor as it would keep any future leaks below your floor level. Not a major thing as that line isn’t used much but just a thought.....