I have a TT and my black flush is on the passenger side about five ft high. "MY" check valve is just inside where the hose connects. its behind my kitchen sink. If you care to do it, unscrew the connection point from outside and see if its right there. BUT,, if you cant get your hands on it, that wont matter. I dont trust using it anymore. Not being able to actually see it working, mines not worth using. And a real pain in the butt to be sure its properly winterized. Just my opinion.
TT: 2018 Coachmen Catalina
243rbs(rear bath) legacy edition
TV: 2017 Ram 1500