By Cheri Sicard
Not all RV odors come from the black tank. Sometimes you can get ghastly gray water tank odor too. The first time it ever happened to me, I was convinced I had a propane leak because of the smell. But it persisted even with the propane system disconnected. Turned out it was the gray water tank odor and thankfully it was easy to fix.
If you have been out boondocking awhile, your gray water can start to smell because of all the food particles, body oils, and soap concentrated in a small amount of space.
In the video below, the RVgeeks talk about this common RV problem and their recent experience with tracking down and fixing an unusual gray water tank odor problem in their rig.
How to keep gray water tank odors out of the RV
- Use a P-trap. Just like in bricks-and-sticks homes, the P-trap in plumbing is designed to keep odors out.
- 360 Siphon roof vent caps that take the air out of the gray water tank and keep it from coming into the RV.
- Air admittance valves sit under the sink and allow air to enter the plumbing system as you use the sink and prevent water in the P-trap from siphoning out
If you are getting odor despite these stop gaps, you will need to ferret out where it is coming from. The RVgeeks say the natural places to look are where there are breaks in the plumbing system. Or perhaps the valve isn’t properly working, for instance.
The RVgeeks encountered such a mystery. Nothing in the plumbing was leaking. All the preventive measures seemed like they were properly working. Nonetheless, when they would move after boondocking, the gray water tank odor would return. They would smell it when they first started driving, but not so much once moving down the highway.
They checked that the valves were working (and in the video, you will learn how to check yours), and the smell did not seem to be coming from any of the sinks. It had them baffled.
Eventually, they noticed that the smell seemed to be coming from behind the kitchen sink in the space between the counter and their slide room wall.
As the kitchen is in the slide, it has a flexible drain hose that moves with it. The RVgeeks say had it not been for this odor, they never would have realized that the top of this drain on their rig had cracked open. The reason it hadn’t leaked was that the crack was on the top of the pipe, which turned it into an aqueduct instead of a pipe.
They never smelled anything while parked because, with the slide room in, the crack would close.
So why didn’t they smell anything when driving down the highway? Because the speed created enough of an updraft through the rooftop vents to take the smell away.
They fixed the issues by replacing the 3’ pipe with a 4’ pipe so it had more room to flex without stress.
While not everyone will have this specific gray water tank odor problem, the video does show that sometimes diagnosing RV issues takes some detective work. By following the RVgeeks on their journey, you might get a better idea of how to discover the root of RV issues you might be having.
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I would venture to say most gray water tank odors are caused by rinsing food products down the drain that accumulate on the bottom of the tank and don’t get flushed out by draining the tank. When we got our motorhome DW started to scrape food scraps from the plates down the drain like she did at home. I caught them in time and put them in the garbage then explained why we don’t scrape the food into the drain. We never had a odor problem in the 4 years we owned it.
I never did that in my former motorhome but it still had gray water odor.
Thank you, Cheri! The RV Geeks are excellent! Thank you for calling my attention to this particular video! 🙂
There is possibly one other place bad odors can come from. Our trailer began to smell after a trip where we used non potable water at a dump station to rinse out the black water tank. I used a long hose and went through the toilet. We cleaned and deodorized with everything I could find. Turned out the non potable water had slipped past the seal and was being held in the base of the toilet. A purchase of a new toilet solved the problem.
We have never experienced holding tank odors when dry camping or driving with waste in our holding tanks. The only times foul waste odors have entered our RV is when dumping our tanks at full hookup RV sites. Since it has occurred rarely and only at some RV parks, never when using a dump station, my thoughts are the RV park waste piping has venting or other problems since our waste hose makes a liquid and air tight connection to the park’s waste plumbing.
The problem is RVs don’t use spring loaded quick vents like mfg housing does. This means instead of the spring loaded rubber stop is open all the time until a water backup forces it closed. You can just as easily unscrew the vent underneath your sink and fill the pipe opening with a plastic bag. It won’t affect the water drainage from the sink and you won’t have a build up of solids in the ext. hose.
Sorry for the typo. Instead of the spring loaded stop staying closed all time to prevent a back draft. It stays open all the time. Only to close when water pressure pushes it closed. I’m sure they use this type because of elevation changes RVs endure. Unless you have a dishwasher the simple fix I stated earlier will eliminate your problem. As far as an undamaged drain system goes. The drain roof vent for RVs is really too low. I think this is because height constraints and esthetics but really unacceptable construction. You’ll find these quick vents under your sink an maybe shower.
There is another source of grey water odor getting inside – the kitchen sink anti-siphon valve (vacuum break) itself. I have found small insects on the valve seat preventing it from closing. Remove the valve, it is threaded, and soak in water, rinse, and reinstall. Do this every year