Question: I have a 2013 27 ft Cougar 5th wheel. After stopping for the day, there is a sewer smell in the undersink area in the kitchen. I checked the P-trap under the sink and its full. Any ideas?
Answer: Our guess is that you have a vent under the sink that is no longer functioning properly. Some manufacturers install a vent that vents to the roof.
Others use a ventless sewer valve (Air Admittance Valve or AAV for short) that is supposed to allow air in, but no sewer gases out. On our RV we have an ventless sewer vent valve that sometimes sticks open and allows sewer gas from our grey water tank to accumulate in the under sink cabinet.
If your RV is still under warranty, then ask the manufacturer or dealer to fix the problem. If you are out of warranty, then it is all on you and fixing the problem can be difficult if the system vents to the roof. If this is the case, take it to a professional to fix the problem.
If the culprit is one of those ventless sewer gas valves, they are easy to replace and some are cheap (what the manufacturers typically use) and others are a little more costly ($25 – $40 dollars to buy). These AAV valves typically just screw on and off, although some snap on and others are glued in place.