Tank odors inside the motorhome

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rickcindy

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Aug 15, 2019
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1
We have been traveling for the past 5 months and have been experiencing sewer/gray tank odor inside the motorhome.  We have done everything we know to do, thoroughly cleaning the tanks, using a couple different types of chemicals, dumping ice into the black tank while driving.  We believe this is a gray tank odor just because of where it seems to be coming from.  We have a bath and a half, and the smell doesn't seem to come from the rv flush type toilet but does smell in the shower bath with a macerating toilet. We have a dishwasher and I do use it fairly often but clean dishes before I fill it.  We have run out of ideas.  Can you help?
 

HueyPilotVN

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Jun 5, 2012
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Lake Havasu City, AZ
As a follow up there are couple of ideas that might help.

Sometimes the pipe that goes from the tank to the roof can slip and fall lower into the tank. If it gets below the waterline or even down to the bottom of the tank it will not vent and could cause your problem.

Another thing that might help is to put a venturi type cover on the top of your vent pipes to help vacuum the odors out of the tanks.
 

ArdraF

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Feb 12, 2006
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10,693
Gray tank odors can be really awful!  Have you cleaned out your shower drain?  Sometimes hair gets down there and clogs it up.  A clump of hair can smell pretty bad!  The kitchen sink also can be the source.  It's hard not to let food particles go down the sink drain and sometimes that can be the source of odors.  My advice is to look for the easy things first!

ArdraF
 

SLOweather

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Dec 2, 2018
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See reply #1. Neither of our vents were sealed between the pipe and the hole in the roof. This can, at times, allow odors from the vent to get sucked back down into the walls.
 

Bill and Debbie

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Jun 7, 2014
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Poulsbo, WA
Do you notice a bit of a smell when turning on the hot water? If you haven't flushed out your hot water tank in a while, you'd be surprised how the scale coming out can smell pretty nasty. Was told to flush our tank every 6-8 months if full timing. Might be worth looking into.
 

Dan de La Mesa

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Oct 18, 2015
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We recently went through the where-is-that-smell-coming-from saga on a cross-country trip. I tried a long list of fixes, and two of them actually seemed to improve the situation. First, I learned that either cracking a front window or leaving the skylight slightly open was a mistake, in that it sucked any odors from the bath up to the cab area. So, windows closed and seal around the front skylight repaired. Secondly, I discovered that the two bolts that hold the toilet to the floor were loose, presumably allowing odors to rise from the holding tank. I tightened them a reasonable amount, and in conjunction with the closed windows while moving, the problem was completely solved. I'm not sure whether this has any bearing on your situation, but it might be useful to others.
 

Henry J Fate

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Jun 14, 2018
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1,979
I would first determine positively what tank odor you are experiencing. Give the gray tank a good cleaning. Fill it about a quarter full of fresh water. Add a good amount of bleach to kill any existing odors and to prevent any new odors. Leave the black tank as it is. If the smell continues, it will probably be the black tank. If it stops, it will be the gray tank. This will enable better troubleshooting.

I have experienced both odors in the cabin. The black tank odor was a bad seal on the water inlet to the toilet. I pulled the toilet and repaired the seal about a year ago and no tank odors still.

I at one point got a very bad gray tank odor. The odor was mostly due to temperature, the time in-between dumps and the lack of good odor control. I found that one of the drain line seals at the tank had dried out and because the pipe it serviced wasn't square to it, it began to leak odors and in some cases water. I replaced the seal with no additional odors in the cabin.

Since then I discontinued the use of advertised tank additives. I wasn't happy with anything I tried unless I used 55 gallons of it. I currently use a mixture of granular laundry detergent and pool shock in the black tank and granular pool shock in the gray tank. Both have produced much better results with good savings in the pocketbook. The gray tank health has increased tremendously using the pool shock. The blue stuff would just mask the odor. Pool shock eliminates it when used properly, easily stored and cheap. The black water will always be foul and relies on good plumbing and venting. It takes too much additives to neutralize the tank. I find that the black water odor will be fairly well controlled initially but slowly gets to its normal foul odor and usually well before a dump.

If the odor turns out to be a gray tank odor, look closely in the plumbing areas in the area you suspect the smell is originating. Use your nose under sinks, inside cabinets where plumbing exists, remove any access panels to plumbing areas and have a whiff. The adavents are a possibility. Each plumbing drain will have a trap. Each trap will usually have an adavent to protect it. Those can usually be found near the trap as high above the trap as possible. The adavent is normally closed but will open when dumping the tank if the tank vent cannot keep up with the flow of water that is exiting during a dump. If a tank vent is exceeded without the adavent, the vacuum would suck the water out of the trap and until the water is replaced, the trap will allow odors into the cabin. In my unit, both the bath sink and the kitchen sink have the adavents in the cabinet below. They did not put one on the tub which I determined as another possible odor leakage from the gray tank. I since upgraded my vent so to avoid that problem and to be sure I always run the water in the tub after dumping to be sure water is in the trap. In order for the adavent to be bad, It would not be sealing properly under normal water usage. I have never heard of one going bad but it is possible.

Black water odors are much simpler to locate. The toilet is always a prime suspect. The bad seal on my water inlet took a little time to figure out. I began to notice that the odor was less if the toilet cover was down. The blade seal seemed fine. I took a whiff one morning at the water inlet and sure enough, it was coming from there. I did a complete service on the toilet and sealed up the water inlet.

 

Frank B

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Apr 23, 2005
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Calgary, Alberta
Could it be something as simple as a drain that has not had any liquid in it for some time? The water in the trap will evaporate and let sewer odors rise.
 

frank1947

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Nov 2, 2019
Posts
38
The odor issue inside the motorhome is really a pain in the nose. I've been using happy campers organic RV holding tank treatment.

https://rvingreviews.com/plumbing/rv-toilet-chemicals-holding-tank-treatment/

We've been full-time RVers for 2-1/2 years, and have had RV vehicles for almost 20. We've used this product exclusively over the last 8-9 years. It keeps the toilet odor-free and is a natural product so it doesn't hurt the environment. To keep your drains free of smell and running freely add a scoop or two when you empty the tanks.
 

Rene T

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May 20, 2011
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Farmington NH
The OP posted this question 3 months ago and never got back to us so we don't know what the outcome was. This is why we always profess to please get back to us for future assistance to other members.
 

Robert K

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Jan 30, 2011
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652
SLOweather said:
See reply #1. Neither of our vents were sealed between the pipe and the hole in the roof. This can, at times, allow odors from the vent to get sucked back down into the walls.

This was the way ours were. I took 1 " foam backer rod availible at Home Depot and stuffed around the pipe. I then caulked that to hold in place , it seems to be working
 

Garyi

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Aug 5, 2013
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Location
Olympia, Washington
WE were getting a bad smell when on the highway. Solved it by adding water to all drains prior to starting out and also by blocking off the drains either with the stopper plug or a flat disc drain stopper. Air flow inside cab was pulling fumes up out of sink and shower drains. I assume the same could be true if you have a washing machine or dish washer. Not sure how you would plug them off though.
 

Swift

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Aug 6, 2019
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I had the same issue with my kitchen sink. In addition, the bottom of the sink lid got wet after driving highway speeds, causing positive pressure in the drain.. I added a Camco RV Cyclone Sewer Plumbing Vent to the roof vent and it fixed the problem, immediately. $18 - $20 on Amazon.  Good luck!
 
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