After re assembly of waste valves and cleaning of black tank rinse, I found a leak at the steel nipple that connects the gray nylon interior piping with the tank rinse outside hose connection.
This nipple was leaking at the threads where it connected to nylon. I had to remove bathroom counter top, and cabient shelf to get access to the fitting. The nipple was so short that just getting ahold of the nylon nut was damm near impossible.
I have included pictures of the parts I removed. First picture shows the whole assembly, piping, vacum breaker and back flow preventer.
2nd picture shows corrosion on pipe nipple, this is where leak was.
3rd picture show detail of vacum breaker and back flow preventer.
I installed a longer nipple and used thread sealer on reassembly.
Result, leak is fixed.