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

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!

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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…. connecting 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!

The piano music is my own performance of Scott Joplin's Maple Leaf Rag from 1899.

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[c.m.]

Briilliant!!! I have had an RV on/off for over 10 years and this is the first time I have heard or seen the P trap trick on the sewer hose!!! There is nothing worse than the smell of sewer in a beautiful campground! LOL Thanks so much for posting this video and sharing your wisdom.

[RVgeeks]

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.

[RVwithTito]

Another great solution that is so obvious that nobody could think of it except perhaps a retired plumber turned RVer. I saw the tip when it was published by haven't tried it yet. Thanks for the demonstration!

[MrRich]

As a full time RV ER and also master plumber I find your solution for the grey water tank with P trap at the bottom of the discharge valve is the perfect solution exactly I find it best information that I found online keep up the good work look forward to more of your updated rv tips and product knowledge the 360 Eliminator vent cap system totally awesome is totally reduced 100% of the gases from the holding tanks as we drove down the road with the windows open it did exactly as you said perfect never have another problem with plumbing gases great job guys

[dunkonu]

We were pretty much forced to do this last week.  The sewer connection we had at AMA in Muncie, IN was higher than the highest point on our sewer hose.  I used the container I use for sewer hose storage to raise the hose above the sewer connection, but because of the ground, and the size of the container, there was a natural trap made. I did not think I was making a trap of sorts at the time, but after watching your video, I will be doing this all the time. Thanks guys!  

[TheCoozey]

Wow, this is a great video!  I have had the sewer gas issue and never thought of making a whole house P-trap like that. 

[TexCynRVLife]

Good to know about the roof vents. I didn't think about that issue in relation to keeping the gray tank open. Thanks!

[gregmacklem]

Great tip. I had the sewer odder problem while leaving the grey tank open and had to shut it. Will have to try the sewer hose P trap.

[comet]

Putting a loop in the hose....what a brilliant idea.

[LifeInSerenity]

What an easy solution. Thanks for sharing.

[thestuffz]

great idea! I was in Calgary west RV park couple weeks ago and didn't notice any sewer smell. I think that each site's hookup has a P trap of it's own just a couple feet under the ground. 

then to dump black tank you just have to undo the P trap, dump, rinse, make the P trap again. genius!

[Jack-Surreal_Panes]

Good info. Just got an old bumper pull so learning as I go. I don't have a fancy support for line but did have a section on plastic c shaped gutter, could use the 4" pvc pipe too. Elevated the gutter with stones so good flow to sewer and did add that trap loop. I didn't like the idea of just laying the tube on the ground. Bad thing about older trailers is there is no fancy tank level, you have to flush and look.

[gailjohnson]

Thank you for the video. Blessings to you.

[J.Cameron.Stuart.Adams.]

I am always telling people to do this. So many assume just because they can't smell it, we can't. However, on warm summer evening when the hot air is park just above us, that nasty smell always makes it's way into my open window to wake me from a dead sleep.

I wish everyone would think of this common sense solution. Along with properly securing their hose to the sewer connection. Ugh... seriously. Especially with today's parks seemingly getting smaller as they add more sites. The park I'm in now is allowing small trailer to use half of a site. I can literally reach out my window and touch the neighboring trailer. I'm not even exaggerating. If he needs me to wash his back, all be has to do is ask. Not that I would oblige. I might pass him my back scrubber. This issue of two RVs just inches apart exacerbates the sewer gas issue. He is in a little trailer and I am in my DRV. Just three feet away at the same level as my bedroom window is his sewer gas vent. Because we are so close, the gases coming out of an ill fitted sewer hose and the vent pipe are not moved or diluted due to a lack of airflow from being too close together. Sure he gets a discount, but I'm the one suffering from his snoring, poor sewer connection, and gases coming out of his vent just three feet from my nose. I dare not complain. The park is full. Bit $110 a night for this is insane. The spaces are so tight my truck is park in an overflow lot a five minute walk away. I'm disabled too. So this walk is difficult despite my younger age.

[scottwall]

Not Legal if your getting technical but in this major California drought you can break a rule for mother nature and run the gray water out at night with a garden hose to the closest tree. Wifey and 2 daughters all have Farrah Fawcett hair so water conservation is a hot topic. Soap is harmless and the little pine tree that is in a struggle to stay alive will appreciate the extra H2O!!!
I did lotsa research on the Wynn poop box and no way am I mixing smashed coconuts to create a compost to carry a box full of poop. See ya Ka flush!
Thank you RV Geeks.

[luckybrake]

Maybe just a reminder to never leave the grey open or the hose p trap position in below freezing temperatures .

[thomasdelbert]

You're effectively creating a whole house trap. These used to be common in houses but not any more. They had a problem with accumulation and backups. I guess if you're in an RV, you probably clean that line regularly, but I would be careful if you're planning on staying a long time.

[jblacktube]

I've heard others say that you want to keep the grey tank closed even when hooked up so that you can flush the hose after voiding the black tank.

[Me-bmht]

Hi
Help me why when i opened the grey water every 3 o 4 days cause we are full timers the black tank show me empty too if i just pull out the valve from the grey water ?

[DeepSnowRider]

Really best thing to do is keep the grey tank closed. It's not hard to pull the grey tank valve to flush for 30 seconds every few days and it's good to have grey water available to flush out the hose if you flush the black.