Mystery vent above kitchen cabinets


Hi everyone I’m hoping someone can help me I have a 2017 BigHorn 3970rd. I made the mistake on our last trip to forget the black tank flush on while the gate was closed I didn’t notice til water started flowing from the roof and water started gushing from black water pipe where it connects to the sewer hose. I opened the storage compartment under the fifth wheel where I could see the pipes leading into the trailer and found no signs of damage. We are now camping two weeks later and I’m getting what seems to be a foul smell like sewer gas coming from this vents. I’m not sure what this vent is for and how I should procedure forward. Hopefully I’m not the only one that’s made this mistake. Any suggestion would be great. Thanks


  • 6F23A3FE-8998-453E-A778-8F0BCD116E90.jpg
    82.3 KB · Views: 82
  • 639FE871-6FEF-4B4B-9331-AF0140DEA6E1.jpg
    74.7 KB · Views: 83


Well-known member
Open the cabinets under the kitchen sink and give a good sniff as well as the bathroom sink. It maybe the Studor valve.
Studor valve is under the sinks, look up. It allows air behind water so the drain can function properly.

The I believe that that vent goes into the area where your furnace is. It allows air to be pushed into the RV from the furnace ducts without causing pressure problems. Don't think you could in an RV with slides. What is back there maybe the area behind your UDC. The vent pipes on the roof may not be sealed at the roof allowing the tank gases to get into that area and then into the living space. We had a similar problem that turned out to be a park problem. The odor would enter the RV when the wind changed directions or when my neighbor emptied his tanks.



Staff member
That looks like the cold air return for the furnace.
If you had sewage leaking out through the roof vent then some of it may have made it into the "attic". The insulated area between the roof and ceiling.
Your AC unit will then pick up the odor.
Remove the roof mushroom vent covers and seal the area between the roof and vent pipe. One screw covered with caulk holds the vent cover.
And if it makes you feel better, you are not alone in forgetting about the flush while the drain valved is closed.



Well-known member
I do not know if anybody has made this mistake but I bet YOU don't make this mistake again. The vent is the cold air return for the furnace as someone has already pointed out. Many times the black tank vent to the roof is not sealed between the pipe penetrating the roof and the roof itself. It is sealed out side but not inside. You also could have pushed some liquid passed the vacuum breaker, which is pretty close to the cold air return by the furnace