2015 Bounder 34T.    How/ where can I access the vent connection to the Black Tank?     Blank tank odor.    The black and gray plumbing valves in the Service bay have moved to the rear about an inch and are no longer centered above the access port.    I filled the black tank by adding water to the vent stack on top of the RV.   Once the tank filled, water leaked  out from the holding tank bay.  (that leak must be where the smell comes from).     

I finally found the problem.   The 1-1/2" ABS pipe between the VacuFlush Pump and the Black Holding Tank had separated.    It was never glued during assembly!  Build up on the pipe showed that it was inserted  about 1/4".    Only took 5 years for it to come apart and allow sewage and smell to escape!