Do You Keep Your RV Gray Tank Open? Closed? How About BOTH?!

TheRVgeeks Plumbing, Water & Sewer 26 Comments

Leaving your RV’s gray valve open when fully hooked up allows you to take long showers without worrying about dumping or filling up the gray tank. But what about sewer smells that can come up from the campground sewer system? Here’s how to get the best of both worlds!

One of the luxuries of staying in a full-hook-up campground is the ability to use water freely for showers, cooking and washing dishes. The sewer connection allows you to leave your RV’s gray valve open, so water can run right out instead of filling up your gray tank.

Of course the black valve can NEVER be left open, since “solids” will build up in the black holding tank when the “liquids” run out. But there’s a fair amount of discussion about the gray valve. Some people recommend that you should never leave the gray valve open either, as it can allow odors from the park’s sewer system up into your RV.

Of course leaving the valve closed means having to pay attention to the water level in the gray tank, and dumping it every few days. Seems like a shame to have to do that when your RV is connected to a sewer line, especially when you’re staying in a full hook-up site for an extended period of time.

Since the drains under every sink and shower in an RV are equipped with a p-trap, leaving the gray valve open shouldn’t allow odors into the RV. The water in the traps blocks odors from entering the RV’s living space. Long periods without use can allow the water in the traps to evaporate, and driving on twisty or bumpy roads can cause it to slosh out. But both of these situations are easily remedied by running a small amount of water down each drain.

There is, however, a pipe with a direct connection to the sewer hose…. leading to the tank vents on the roof of the RV. This can allow air from the sewer system to come up through the roof vents. If you’ve ever smelled sewer odors in a full hook-up campground, it’s possible that someone’s RV is venting the park’s sewer system out through their roof.

In a recent RV Travel newsletter, we read about the simplest way imaginable to enjoy the luxury of a full hook-up RV park. You can leave your gray valve in the open position so water runs right down the drain. You don’t have to pay any attention to how full your gray tank is and you don’t have to dump it every few days. But there’s no chance for sewer odors to escape either. It’s the best of both worlds.

Watch the video to see how we did it!

Please use your full hook-up powers responsibly and don’t waste water!

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Just a brief follow-up… Although this wasn’t a video about tank dumping, it is related, and there were some comments and questions about it. If the gray valve is left open, there isn’t any gray water available to flush the sewer hose after dumping the black tank. Here’s how we handle that.

Conserving water and monitoring tank levels are just part of life for most RVers, so it’s a luxury to be able to forget about it once in a while. When we’re in a full hook-up RV park for an extended stay, leaving the gray valve open allows us to take longer showers, while completely ignoring the level in the gray tank. We just use the trick we demonstrated in the video to prevent sewer odors from coming in through the open gray valve.

Then all we need to do is keep an occasional eye on the black tank level. Since we often take the load (sorry) off the black tank by making periodic use of the park’s bathrooms (as long as they’re clean), it takes a solid (sorry again lol) two weeks or more to fill it up. When it shows 3/4 full, we close the gray valve for a day or two, allowing gray water to accumulate in the tank.

When we’re ready to dump, we take a few seconds to put the entire sewer hose back up on the sewer hose support, then dump both tanks, black first of course. Plenty of water has now accumulated in the gray tank, allowing us to flush the sewer hose after dumping the black tank. When we stay in one place for an extended period, we appreciate being able to completely ignore both tanks for two-plus weeks at a time. This way of managing our tanks allows us to do that.

This is a perfectly fine way to handle shorter stays too. After boondocking for extended periods, we’ll sometimes treat ourselves to the luxury of full hook-ups for a week or so, leaving the gray valve open and using the same sewer hose technique. We simply close the gray valve a day or two before we’ll be leaving the park, and dump both tanks on the morning of our departure.

We're handy RVers, not professional technicians. We're happy with the techniques and products we use, but be sure to confirm that all methods and materials you use 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.

We sometimes receive products for evaluation at no cost, and The RVgeeks are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to and affiliated sites. But our opinions are our own, you won’t pay an extra penny, and we only link to products we personally use, love and can recommend to friends with complete confidence.

Comments 26

  1. I been living in this trailer for almost a year the sewer system of the whole trailer park is mess up so every time is clog up the sewer water come back up on my bathtub is discussing but when I do call the land lord she said is not her problems now what I do

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      Sorry to hear. Obviously your park has major sewage issues. We would suggest that until they fix the problem, you keep you gray valve closed to prevent the sewage from backing up into the trailer. Hopefully when you go to dump it each day, it won’t come up instead of going down.

  2. Hello we have been living in our trailer for a year now and was wondering if we can leave our toilet tank open…. We don’t travel it’s our home.
    thank you .

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      Hi Elena! Definitely not! If you leave the black tank valve open, the “liquids” will run out and the “solids” will pile up, dry out, and harden into a smelly mass. That’s commonly referred to as “pyramiding” and it’s a horrific mistake to allow that to happen.

  3. My husband and I are new to our fifth wheel trailer….. We will be living in it while building a house. We had to evacuate for Hurricane Irma without our fifth wheel trailer … So I thought to add weight to the bottom to try to take the winds I would fill all 3 tanks .. Fresh, gray, and black. I think I over filled the fresh water… Does it go into black and gray if it is filled too much? So i filled them and she stayed upright! home and emptied all the tanks (all fresh water)…but my gray tank is still saying it is at 1/3 on the interior monitor?…the gray water tank valve is stuck in the open position so when I took the cap off the gray started flowing out immediately. I got the black valve open (now they are both open) and it drained clear. There were 2 caps that went to the water heater and it drained and another cap further under the trailer in more… Probably for sink? As it is above where the cap is. And it drained its water. I don’t know why it is still reading that there is water in the gray tank… Any suggestions?

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      Hi Deborah. Glad your RV made it through OK. First, it is extremely unlikely that your freshwater tank overflowed into your gray tank, as the overflow almost certainly goes onto the ground. As far as lights showing on the tank that you know is empty, the most common reason is a clogged sensor. Use this link to watch our video about cleaning gray tank sensors and see if that helps:–c

  4. Somebody please help. Left my camper the other day no ac on came back to an ammonia smell that nearly knocked me down. All I could find on that odor was my fridge but it’s working great and no odor. Turned the ac on and smell was horrible again. AC didn’t seem to cool. Then the next evening turned ac back on cooling great. About 5 hours later woke up tp the horrible ammonia smell. I do not use my black tank because I have my camper behind my moms to stay and take care of her and was not living in it. I use the shower and wash dishes and leave my grey tank open. I can’t figure out where the smell is coming from and if it was an ac leak it would not cool. Been 3 days now fridge still working great. I’m at a loss. My grey tank reads 3/4 full while open and fresh water tank I never used says 2/3rds full. Does anyone have any idea what could be going on? Only smells when I use ac. Thanks

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      Not to be alarmist, but if that ammonia smell is coming from the refrigerator, it could be very dangerous. You’ve said it’s not coming from there, but you should confirm that, as it’s the most dangerous source of an ammonia smell. RV fridges of course us ammonia to cool, and leaking ammonia is potentially flammable or explosive. If it is leaking, the fridge might still be working until it all leaks out. The first thing we would do is see if the smell is particularly strong outside the RV at the vents at the back of the fridge. If you smell it strongly back there, we’d suggest shutting down the fridge until you can have it looked at by a professional. Bi-fuel (propane/electric) RV fridges are just about the most complex piece of equipment on any RV, and not easy to service or troubleshoot for the average person.

      If you don’t smell ammonia the strongest behind/under/around the fridge, it may be from some other source. It’s suspicious that your a/c didn’t cool…. but then it did. The contents of a black tank, left long enough, might have an ammonia-like smell, but from what you’ve described, it doesn’t sound like a likely source, since you don’t use it.

      Are you the first owner of this RV? If not, how long have you owned it? Have you had the problem all along, or has the RV, used in the same fashion over a long period, just started having this problem recently? We’re thinking that if you started using it recently and the contents/condition of the black tank is unknown (used by a previous owner?), you could have a sludge build-up in the black tank. Then you turn on the a/c and it pulls in odor from the black tank roof vent near the a/c unit. Since you said you don’t use the black tank, have you ever opened the toilet valve to see if the odor is coming up out of the toilet/black tank?

  5. but you close the black one before opening the grey one, right?
    the people who i got my camper from left both open…isnt that a no-no?
    (still learning, here)
    appreciate your articles & vids :)

    1. Post

      Hmmmm…. leaving the black valve open is pretty much a cardinal sin. That allows the “liquids” to run out of the tank, leaving the “solids” behind to form a pile (known as “pyramiding”) which can be very difficult to remove… and a major cause of tank odor.

      For a pre-owned RV with a black tank that may have been maintained in a less-than-optimal manner, we’d suggest you start by following our flush & clean procedure ( ). After that, fill the black tank with water and some Happy Campers Extreme (available on Amazon: and let it soak for a few days. Then flush it out again. If you see a lot of debris coming through your clear sewer elbow, you might want to flush it again and then do a second Happy Campers Extreme treatment.

      To answer your first question, yes… after emptying and flushing the black tank, always close the black valve before dumping the gray tank.

      Hope this helps. Please let us know his you make out. ☺️

      1. thank you very much. earlier this year, i stuck a garden hose through the toilet and flushed it out til it was clear (as far as i can see)..but your recommendation may be good to follow up with, too..i was concerned that somehow the sewage could leak into the gray, maybe travel up into my water lines…i dont know how long they had this one. traded my 5th wheel for this one, cause i wanted a bumper pull..but i already knew about closing them and not having both open at same time. when i told them this, they seemed surprised

        1. Post

          If you’re not getting any odor from the black tank, you’re probably fine. And don’t worry about water from the gray tank getting into the water lines. That’s not a problem. That said, you should indeed dump one tank at a time (black first) and close that valve before opening the gray valve. Safe Travels!

  6. Forget netflix, I’m a newbie and find myself watching your videos back to back to back….and might I say, your voice reminds me of the ‘ How it’s made’ narrator.

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  7. Interesting you just did this video. I have been RVing for all of my life. Age 0 to 52. Recently most states have been putting laws in place that you must seal your hose to the campground sewer connection. Just last weekend I was called out for not doing this for the first time. My trailer has gray water vents that have one way valves that vent from inside the coach. I feel it is in my best interest not to seal the hose and let any gasses escape around the sewer connection so I do not suffocate from methane. Also if there is a backup in the parks system, I rather not have it backup into the coach. Your thoughts?

    1. Hi John. We have the same one-way valves under all of our sinks, but since they’re designed only to allow air to enter the plumbing system, but not escape from it, there should be no issue with sewer gas entering the RV’s living space. Of course if they aren’t working properly, you’ll know, since it will smell like black or grey water under the sink at times. If tat happens, they’re inexpensive and easy to replace.

      In our 11+ years of full-timing, we’ve never heard of a sewer system backing up into RVs, but if you’re concerned about it, simply leave your gray valve closed, even when your sewer hose is sealed to the park’s sewer outlet. Then you’ll be in the same situation as when dry camping…. basically completely self-contained. Then just pull and re-close the gray valve every couple of days as needed. The laws about sewer hoses being sealed tightly to the outlet is to prevent pollution from black or gray water from escaping onto the ground in an RV site (we’ve seen plenty of people get black and/or gray water on the ground in their site). Enough of that will make the site, shall we say, less than appealing, not to mention polluted. ;-)

  8. This goes to show that useful tricks don’t need to be complicated! Keep ’em coming… :) We love it.

  9. We find your videos to be an excellent source of information, often answering questions we didn’t even know we had!

    I very much appreciate your style and “spirit” – please keep up the good work! Marv

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