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Old 10-26-2016, 10:50 PM   #1
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Mild sewage odor from 1/2 bath

This odor appears to be coming from underneath the sink. I have run water in the sink to ensure the trap is filled, flushed the toilet several times and checked to make sure there was a few inches of water in the bowl. It still stinks, and I can smell it walking by with the door closed. Underneath the sink, I found what appears to be a breather cap on the top of the vertical pipe on the right, and it was very loose. I've screwed this down tight, but am not sure what purpose it serves, or if it should be tight. Since it is after the trap, my guess is that it vents the gray tank into the storage area under the sink.

Also, what are the 2 pex lines on the left, and what is the valve or connector that joins them? I haven't removed the green tape to look underneath it, but am pretty sure that having tape there isn't normal.
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Old 10-26-2016, 11:29 PM   #2
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Both sinks in the master bath have vent caps, and they are loose. I also had the gray valve open in preparation for a couple of loads of laundry, and wonder if fumes from the sewer connection could be wafting up into the gray tank and then up through the vent cap into the coach. I have since shut the gray valve but the half bath still smells pretty bad. A lot worse than I would have thought a gray tank should smell.
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Old 10-27-2016, 12:45 AM   #3
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The Grey tank can smell almost as bad as the Black tank. You are correct that the cap on top of the drain line is a vent. You can purchase a replacement at Home Depot or ?? - pretty inexpensive.
We find if we run a gallon of hot water mixed with a cup of Oxyclean down into the grey tank it will take the smell away for a while.
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Old 10-27-2016, 05:24 AM   #4
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The vent is called an air admittance valve. It lets air into the drain system and is supposed to be one-way. They fail with age, but that shouldn't be the issue on a '17 model. It should not be loosely fitted into the pipe.

For reference, I had the same or similar issue and the problem disappeared when I replaced those valves.

Can't help with the green tape. Sorry. Unless someone else knows what those pex lines are for, I'd email Newmar with that pic attached and ask.
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Old 10-27-2016, 06:00 AM   #5
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The PEX lines are your black tank flush line and the valve is a back flow preventer or vacuum break.
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Old 10-27-2016, 07:00 AM   #6
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I have the same issue, same valve with my 2016 Bay Star Sport, have replaced the valve and it still happens. Mine is in very tight.
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Old 10-27-2016, 07:13 AM   #7
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I can't help with what the particular lines are but I'd suggest you treat both your grey and black water tanks with Happy Campers. The grey tank can smell as bad as the black tank, and after trying multiple treatment products in 30 years of motorhoming, this is BY FAR the best product we have ever used. It's available on Amazon in a variety of sizes.
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Old 10-27-2016, 07:46 AM   #8
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Quote:
Originally Posted by USMCRET View Post
The vent is called an air admittance valve. It lets air into the drain system and is supposed to be one-way. They fail with age, but that shouldn't be the issue on a '17 model. It should not be loosely fitted into the pipe.
That makes sense. The valve should only open under negative pressure and shouldn't vent anything into the coach. After hand-tightening this valve and closing the gray tank last night, the smell is now gone. I'm going to open the gray again today to see if the smell returns, but it makes sense that loose threads on the AAV could have allowed bad smells to leak through.
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Old 10-27-2016, 08:29 AM   #9
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Sounds like you may have solved the problems tightening the vent caps.
If when opening the Gray valve outside, to sewer connection and the smell comes back your gray tank will empty and the sewer smell will be coming from the campground sewer system which can effect your health.
Give a call to Newmar to alert them, this is serious.
You should be able to leave Gray tank open for showers and laundry use.
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Old 10-27-2016, 08:53 AM   #10
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Have had the same issues a couple of times on my old 03. The technology does not appear to have changed to this day. Folks are right about the Air Admittance Valve. It should be tight but just hand tight so it can be easily removed. These are very common in residential applications and can be found at most stores such as Home Depot etc. They are a simple device with a rubber flap and light spring but for some reason on an RV application they seem to want to not function as designed on occasion. I have removed mine and run warm water through them and kind of run my finger around under the rubber flap a bit when they malfunction. This seems to work.

The other gizmo that has the green tape over it is called a Vacuum Breaker Valve. It should not be taped. It's purpose is to stop water backflow from the Black Tank into the fresh water line when you use the black tank flush dumping your tanks.
I have had this Valve leak a couple times and pour water down the line into the basement. Fortunately, I had a plastic storage tub below with my spare oil/antifreeze etc that caught the water and no damage done. They are an expensive Valve to replace. After the second one, a plumber friend put me on to a much better product that is used on such things as residential hot water tanks. I have had no trouble since.
I park my coach inside but one of the common causes for failure of this Valve is freezing during winter storage. It is often overlooked during the winterizing process. The brass replacement is not as prone to freezing as the plastic one.

My attached link is Amazon but they also can be found at a Home Depot type store should it give you grief. If you do use this Valve, it requires the purchase of two 1/2" NPT (Brass or Plastic) nipples to connect to the water lines.


https://www.amazon.com/Cash-Acme-173...vacuum+breaker
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Old 10-27-2016, 09:07 AM   #11
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Sounds like you may have solved the problems tightening the vent caps.
If when opening the Gray valve outside, to sewer connection and the smell comes back your gray tank will empty and the sewer smell will be coming from the campground sewer system which can effect your health.
Give a call to Newmar to alert them, this is serious.
You should be able to leave Gray tank open for showers and laundry use.
Some sewer connections are raised such that the hose forms a natural trap once you empty the grey tank once. But, others that are lower allow an open connection when you leave the grey dump Valve open.
I use an expandable rack for my sewer hose that elevates it. At the end, I allow the hose to drop down off the rack to the ground and then up into the connection to form a trap in the hose so you don't get odor back from the sewer.
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Old 10-27-2016, 09:14 AM   #12
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Thanks for the added information Dennis always helpful.
Will add this thread to QT's # 3 -- Problem Solving" busy this morning.
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Old 10-27-2016, 09:35 AM   #13
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Thanks everyone for your advice. No smell at all this morning, so I've opened the gray tank valve and am about to leave the coach for the day. All of the air admittance valves are hand-tight (all of them were very loose), so it will be interesting to see (smell) how things are when we return tonight.

As for the green tape... I have removed it. Somebody took great care to very carefully tape the heck out of the valve, which makes me wonder why it was done.
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Old 10-27-2016, 09:19 PM   #14
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The smell is back...

We came back to the coach tonight after being gone for the entire day, and there was no smell in the half bath. Absolutely nothing. But... after having a shower, I walked past the half bath (door closed) and I could smell it again. The odor is definitely stronger underneath the sink where the plumbing is.

So I have closed the gray valve again. We are out again all day tomorrow, and I'll have a shower again tomorrow night when we return. If the smell is gone when we come back, but returns after the shower, I'll know it doesn't have anything to do with the gray valve being open or closed. If that's the case, I will try switching the vent caps for one in the master bath and repeat the process.

The only thing I can think of is a faulty vent cap, and the negative pressure from running the shower in the other bathroom is somehow causing it to open, and it is sticking open.

Does anyone have any other ideas or suggestions?
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