My 2008 Salem kitchen sink does not have an outside vent. It is vented under the sink with a flapper-type vent. When I leave the gray water open, it fills the camper with a sewer smell....what is wrong, and what can I do other than keep that closed all the time. When I leave the gray water open, I don't open the black water.
ANSWER: Hi Al, the vent that is under your sink is known as an Air Admittance Valve, it is also known as an inline vent or cheater vent. It is used in some RVs and Mobile Homes in place of a roof vent.
When you drain water out of your RV's sink, the draining water creates suction (vacuum effect) on the valve, which then opens and allows air in the pipe, which in turn allows the water to drain freely. When the water is done draining, the valve is supposed to close tightly and seal out any sewer smell or, in your case, gray water smell from coming in the RV.
Based on your description it sounds like your valve is not sealing properly and may need to be replaced. Replacing this valve is fairly simple in that in most cases the valve just screws onto the pipe. All you will need is a big pair of slip joint pliers to help unscrew your existing vent. To install it all you do is put some Teflon Plumbing Tape on the threads of the new valve and tightly screw it on.
Look at the video below to learn how these vents can start releasing a sewer smell in your RV.
The odor you smell from the gray water tank is usually from decaying food particles in the gray water itself. You might want to also start using some Enzyme Holding Tank Treatment in both your grey and black water tanks. The enzymes in these treatments digest waste and work quite well to minimize holding tank odors as well as being environmentally friendly.
IMPORTANT NOTE: If you have replaced the Air Admittance Valve and you still have a sewer-like smell in your RV, you should check the compartment where your RV's House Batteries are stored. Your house batteries could be low on acid and/or boiled out from overcharging. The boil out or low acid can produce a strong sewer-like smell in your RV.
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