Welcome to the forum is a great place to get your questions answered. Do you have two separate black tank dump valves? If so easy check is to hookup the flush and open one at a time and see if they flow water while flushing and you will have your answer. Let the forum know what you find out.
Jake my sidekick (yellow Lab) 10/04 - 05/20
2017 RAM 2500 CC 4X4 Cummins Diesel
2016 Flagstaff 26 FKWS
AF&AM & El Korah Shrine of Idaho
I bought the tornado rinser or whatever it was called. I had the hose connection installed just beside the rear tank pull handles. I had the shop install it above the underbelly but below would have been just as fine.
Worked well for 6 years of ownership. I carried 2 of the black expandable hoses and a 4-way water manifold for the campground spigot/water source.
Officially a SOB with a 2022 Jayco Precept 36C
Checkout my site for RVing tips, tricks, and info | Was a Fulltime Family for 5 years, now we're part-timing on long trips