That's what I told her. She got a plumbing schematic from Monaco that only shows one roof vent to the tank. I spoke to Monaco on the phone and they confirmed the single vent. They later changed the design, because of the same problems she was having. Asked about a retrofit, they said yes at her cost.
Chuck & Teri, 1999 35 ft. Dolphin 5350, F53 Chassis with tag axle, Chassis build date 1/99 in Mexico, Banks System, Trans Command, Air Lift Air Bags on rear, Koni Shocks, Blue OX TruCenter, TigerTrak track bars front and rear, Roadmaster 1-3/4" rear auxiliary sway bar, 2013 VW Passat TDI SEL Premium, 1994 36 ft. Avion 5th Wheel. FMCA #F430129