This post may contain affiliate links.

As badly as gray water tank odors in an RV can stink, their source can also be very difficult to sniff out! We’ve troubleshot a few different gray water tank odors in our RV over the past couple of decades, and we’ve managed to address them pretty easily. But recently we were faced with a new and highly elusive gray tank odor in our RV that required some serious sleuthing.

So, grab your Sherlock Holmes hat and magnifying glass, put on your wrinkled Columbo coat, tap into your inner Angela Lansbury/Jessica Fox, and sleuth along with us (yeah, we know there was no murder involved in this episode, but honestly – as gray water tank odors go, this one was a killer!).

Why Does My Gray Water Tank Smell?

Every RVer understands clearly why the contents of an RV black tank would smell. 💩 Less clear is why gray water would stink as badly as it does. The reason is the mix of the contents.

Think about what goes down your sink and shower drains. Bacteria-filled dishwater, food particles, body oils, and soap. When this combination sits for any period of time, it’s a recipe for some deadly odors, especially if you’ve been out boondocking for a couple of weeks as we often do. The combination of long stays without dumping, and reduced water usage to enable the long stays, makes for a toxic brew.

Sure, there are ways to mitigate SOME of the odiferous contents of an RV’s gray water tank. You can be diligent about wiping food from plates, pots, and pans prior to washing them in your kitchen sink, for example. You can also use a product like Happy Campers holding tank treatment, which we’ve used and appreciated for a long time.

But usually, when gray water tank odors escape from the gray water tank and invade your RV’s living space, you’ve got an issue that goes beyond the tank itself.

How Do You Get Rid of the Gray Tank Smell in an RV?

Having sleuthed this issue out in the past, we know that there are many ways for gray water tank odors to invade an RV. Likewise, there are several ways to get rid of the odors and to prevent them. We’ve been living in an RV full time for 18 years, after all. This isn’t our first gray tank stink rodeo. We’ve got some experience here. Let’s take a look.

Sleuthing Out the Culprit of Gray Water Odors

Let’s see if we can solve the latest gray water tank crime by looking at the evidence and ruling out the suspects one by one.

1. Colonel Mustard in the Kitchen with the Air Admittance Valves

The first time this happened to us, our air admittance valve had failed. We created a post and video as a result of our experience in which we show you how to repair this issue, so you’ll want to check out if you’re troubleshooting a similar odor.

One of air admittance valves under the sink
Air admittance valves are important components of every plumbing system, whether residential or RV.

Air admittance valves are critical components of all plumbing systems, residential and RV. They allow air into the system through a one-way valve, allowing water to flow smoothly, and preventing the formation of a vacuum in the plumbing system. Without them, a large flow of water down the drain could siphon the water out of the p-trap. If that happens, odors from the gray tank can escape through the drain in your sink. And that’s exactly what happened to us, THAT time.

Your air admittance valve is a key suspect if you’ve got gray water tank odors in your RV. We replaced our air admittance valve and the problem was solved.

Studor 20349 Redi-Vent Air Admittance Valve with ABS Adapter, 1-1/2- or 2-Inch Connection
  • Compact air admittance valve with ABS adapter; ideal for a single fixture or group of fixtures up to 20 DFUs (drain fixture units) on a branch
  • Creates ventilation that prevents the loss of water seal in trap

2. Miss Scarlet on the Roof with the Plumbing Vents

Another possible suspect to consider when you’ve got a gray water tank odor in your RV is the plumbing vent. Depending on the size of your RV, you may have one or two (typically, there’s at least one vent for each black & gray tank in your RV, although some manufacturers plumb the lines together to a single vent penetrating the roof).

We’ve experienced this problem as well, and again we created a post and video about replacing our plumbing vents which addressed the problem for us – THAT time.

Adequate air circulation is an essential part of the design of an RV. Most RVs have several rooftop openings and items that are dedicated to the proper movement of air. At least one of these openings on every RV is an RV plumbing vent. In our case we have three, and once we replaced them all with 360 Siphon vents, the problem went away.

360 Siphon vents come in black and white and are, by far, our favorite plumbing vents. The technology is largely unmatched for carrying odors up from your gray tank and out of your RV… without requiring any power or having any moving parts.

Lippert 360 Siphon RV Roof Vent Cap
  • ELIMINATES ODOR - Exhausts odors out the roof vent before they have a chance to invade your RV
  • COMPATIBILITY - Engineered for a universal fit, the 360 Siphon is compatible with all RV vent caps
Lippert Components 389381 360 Siphon Roof Vent Cap - White (Gen 2)
  • Eliminates Odor - Exhausts Odors Out The Roof Vent Before They Have A Chance To Invade Your Rv
  • Compatibility - Engineered For A Universal Fit, The 360 Siphon Is Compatible With All Rv Vent Caps

These vents solved our issue back then, and our RV has been stink-free ever since…until now! This time Miss Scarlett is not the culprit for us, but if you’re experiencing a gray water tank odor in your RV, you may wish to consider switching to 360 Siphon vents.

Again, check out our post and video – they explain everything. If you’re capable of accessing your RV’s roof, all you’ll need to do the job are a couple of basic tools and a caulk gun loaded up with some Dicor Self-Leveling Lap Sealant, and you’ll be good to go for this simple and highly effective DIY project.

HOWEVER – we had to continue to sleuth because this was not the issue for us.

Sniffing around to identify the location of a gray water tank odor in RV
When sleuthing a mysterious odor, putting your sniff detector to work is important!

3. Professor Plum in the Kitchen… Sniffing Around For Clues

When you’ve got an odor coming from your gray tank into your RV, it makes sense to look at any area of the plumbing system where there’s an opening (like the air admittance valves or the plumbing vents).

But if you’ve troubleshot all of the open areas of your plumbing and you STILL haven’t solved the problem, where else could you look? Surely, the odors couldn’t be coming from any of the areas where there are solid pipes, because if a broken pipe was the culprit, you’d have a water leak somewhere. OR WOULD YOU?

Let’s sift through the evidence in our case:

  • Air admittance valve? No problem.
  • Plumbing vents? No problem.
  • Leaks? None.
  • When did we get the odor? Mainly when we would pull away from an off-grid site with a half or full gray water tank, after a long period of boondocking.
  • Did the odor continue as we were driving down the highway? No.
  • When was the smell the worst? As soon as we started pulling away from the campsite.
  • Did it happen when we pulled away from a campground with full hookups? No, because we had an empty gray tank.
  • Where is the odor specifically coming from? From behind the kitchen sink and behind the kitchen slide, in the space between the wall and where the slide comes in.

Aaaaaah HA! It’s Professor Plum in the Kitchen! Watch the video below for more!

Our kitchen is on a slide. For this reason, the drain has to have a flexible section of pipe that moves with the slide as it extends and retracts. In fact, about ten years ago we replaced our flexible PVC drain line because we had a leak in that area. But this time we had no leak at all. That was the real mystery.

However, as it turns out, our flexible pipe had flexed so frequently that the pipe had indeed cracked, but it had cracked on the TOP of the flexible PVC pipe.

The crack in a sewer pipe that let a BAD gray water tank odor in RV
Over a ten-year period, this flexible PVC pipe cracked open on the top.

So, we didn’t have a leak because the water was contained in a little gully of pipe that served as an aqueduct as the water flowed through it.

Water flowing through our cracked-open sewer pipe... no leak, but a bad gray water tank odor in RV, for sure!
Because the pipe cracked on top, it formed a gully on the bottom of the pipe through which water could flow without leaking.

The issue only occurred when the slide was IN/RETRACTED. When the slide was extended, and we were stationary at our campsite, we wouldn’t be smelling gray tank odors. That’s because with the slide out, the flexible sewer line was bent upwards and the two sides of the crack would be compressed together.

When retracting our slide, the flexible pipe would bend and open a crack that allowed gray water tank odor in RV
Here you can see the crack in the top of the sewer line closing up as the slide was extended… which is why there wasn’t any odor when we were stationary.

If you’re wondering why we weren’t smelling the gray tank odor when we were traveling down the highway, it’s due to the fact that the rapid flow of air across our 360 Siphon vents created such a strong updraft through the plumbing system that it would pull the odorous air up and out of the RV.

While this is unlikely to be the result of a mystery that you find yourself troubleshooting, it’s worth having a heads up in case you find yourself scratching your head over a gray water tank odor in your RV.

In our case, the way we resolved this issue is by replacing the 3-foot flexible PVC pipe. This time, we’re using a 4-foot length to allow the pipe more room to flex without stressing the PVC.

But if you’ve ruled out the air admittance valves (we show you how to test that in the video embedded above) and you’ve got high-quality vents like the 360 Siphon vents installed, and your issue isn’t in the plumbing situated in a slide like ours, there are other ways to address gray water tank odors in your RV.

How Do You Fix a Gray Water Tank That Smells?

Another way to deal with gray tank odors is to clean your gray tank sensors. Cleaning the sidewalls of the tank may be very helpful in getting rid of odors, as the buildup of organic matter and bacteria over time can lead to a nasty stench.

In this post, we show you four different ways to clean your RV tank sensors, including having your tanks pressure washed, especially if that’s never been done.

Conclusion to Our Sleuthing

We thought this post and video were worth creating in case the information is helpful to even a few of our fellow RVers seeking to solve The Mystery of the Stinky Rig. Don’t just blame Mrs. Peacock in the library with a stink bomb, get out your sleuthing hat and start sleuthing, armed with our posts and videos.

Geek Out with Us Every Week

Join our newsletter to learn about all things RV-related. Every week we offer free tips, tricks, product reviews, and more to our online community of RVers. So, whether this is your first time on the road or you’re a seasoned expert, we’d love for you to geek out with us!

We'd Love It If You Shared This!

Notify of

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Inline Feedbacks
View all comments

Sometimes we receive products for evaluation at no cost and may use affiliate links to the products and services from which we earn commissions. For example, as an Amazon Associate, we earn from qualifying purchases. That said, it's important to us to let you know that our opinions are our own. We only recommend products we believe deliver real value and that we can confidently recommend without reservation. You also won’t pay an extra penny by using our links. Thanks so much for supporting RVgeeks as we work to create helpful RVing-related content that we hope enhances your RVing life!

Even though we're handy RVers, we're not professional technicians. So although we're happy with the techniques and products we use, you should be sure to confirm that all methods and materials are compatible with your equipment and abilities. Regardless of what we recommend, consult a professional if you're unsure about working on your RV. Any task you perform or product you purchase based on any information we provide is strictly at your own risk.

You May Also Like