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Old 08-11-2022, 03:37 PM   #1
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Sewer gas problem

We recently purchased a used repo 2017 blue ridge and really like it but it has one problem that I just can't figure out. We can only get about 2 days use before having to dump the black tank. It lets us know when it wants to be dumped as every time you flush it fills with sewer gas. Yes, the entire coach. Did notice that if I only hold the flush pedal enough to allow the liquid to go down but not far enough for an air gap to form there is no smell.

All dump valves always closed. No water leakage anywhere. Also, when dumping tanks the rv fills with sewer gas.

There are only 2 of us so we are not overloading the tank. Have had rv's for almost 30 years and never had a problem quite like this.

Anyone else have a situation like this or suggestions on where to look?
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Old 08-11-2022, 03:46 PM   #2
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The first place that I would suggest looking would be the vent stack up on the roof of your unit. The vent for the bathroom is normally very close to the bathroom but on the top of the unit. I would suggest removing the vent cap and looking down the pipe with a flashlight being very careful to not drop the flashlight and make a bad situation worse. It is common for the vent to be disconnected from the tank. You may want to run water down the vent and make sure that all the water makes its way to the black tank.
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Old 08-11-2022, 03:51 PM   #3
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Angry Gas Smell

I would check to confirm that the black tank vent is clear and not plugged with something. One may need to remove the vent cap on the roof and run a plumbers snake through it.

Since it is a used unit, one has no idea how much solid matter or anything else has accumulated in the tank. A good high-pressure washing inside the tank would likely be necessary. For this, I use my pressure washer with a 45-degree bend in the wand just before the spray nozzle. Hold the flapper open, insert the wand, turn on the spray and swish it around a few times. You might be surprised what comes out on the other end via the dump valve.

I've seen houses where the owners knew they were up for repo. The residents poured cement into the toilets and other plumbing areas.

Bob
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Old 08-11-2022, 04:31 PM   #4
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I suspect some sabotage by the previous owners but have had the tank cleaned several times by professionals and hope it is all clear. Can't get a look into the tank as it is a long pipe from the dump valve and the toilet has a curve pipe so no direct look there either.

I replaced all 5 of the vent caps on the roof and none showed signs of tampering, still had the original seal around the screw. I will go up on the roof tomorrow and look down the pipes again. Too hot today.

Ordered new air vent caps for under the sinks and will get them tomorrow.

Just hoping someone has had this problem before and fixed it. It's almost like the gas is venting straight into the ac ducts as it is almost instantly throughout the coach.
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Old 08-11-2022, 05:20 PM   #5
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This picture shows how the vent connects into the black tank. My fear is that the connection of the vent to the black tank may be loose allowing the gas to escape.


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Old 08-12-2022, 10:02 AM   #6
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Thanks for the diagram, I am just trying to figure out why after just 2 days I get the sewer gas. I empty the tank, flush it and we are good for a couple days then it acts like it reaches a vent pipe or something and burps gas inside. And of course, everything is hidden inside walls or subfloor for easy viewing and maintenance....
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Old 08-12-2022, 10:53 AM   #7
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I am having the same issue on my TT. I get a couple more days that you, but I would expect to get more than 10 full flushes (5 gal.) in a 36 gal. tank. I removed an access panel in my bathroom and found where my vent passes through the floor to the black tank. Unfortunately I cannot see the connection to the tank. I know the connection is tight as I cannot rotate or wiggle the pipe, and based on my observation, the pipe is not secured to anything other than the tank connection (not even secured to the roof).

My suspicion is that the vent pipe protrudes into the black tank further than it should, reducing the 'headspace' between the water surface and the vent inlet. Once the water level reaches the vent inlet, the vent is no longer functional.
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Old 08-12-2022, 11:26 AM   #8
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Quote:
Originally Posted by BrandonSmith View Post
I am having the same issue on my TT. I get a couple more days that you, but I would expect to get more than 10 full flushes (5 gal.) in a 36 gal. tank. I removed an access panel in my bathroom and found where my vent passes through the floor to the black tank. Unfortunately I cannot see the connection to the tank. I know the connection is tight as I cannot rotate or wiggle the pipe, and based on my observation, the pipe is not secured to anything other than the tank connection (not even secured to the roof).

My suspicion is that the vent pipe protrudes into the black tank further than it should, reducing the 'headspace' between the water surface and the vent inlet. Once the water level reaches the vent inlet, the vent is no longer functional.
Typically when the black tank canít vent thru the roof when you flush the toilet it will burp. The air being displaced by the flush water has nowhere to go but up thru the toilet bowl flush opening. Does your toilet burp when you flush it?
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Old 08-12-2022, 11:40 AM   #9
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You're putting black tank treatments in the tank? Have you considered replacing the toilet itself? What kind is it? There is a plastic ring (like the wax ring on a residential toilet.) that frequently fails.
You've definitely got a puzzle.
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Old 08-13-2022, 01:09 AM   #10
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Thanks for your input, I did replace the toilet a couple months ago but mainly because it was kinda nasty looking. I haven't really noticed any burping but when it is polluting the inside of the rv with every flush I did notice that if I only open the flush valve enough to let liquid down without forming an air opening I don't get the stench.
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Old 08-13-2022, 01:13 AM   #11
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Brandon, You are thinking of what I think is the problem, the vent pipe is sticking too far into the tank. And of course, that is the most expensive option to fix. And the design of the black water tank system makes it extremely difficult to check by camera snake.
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Old 08-13-2022, 07:50 AM   #12
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Your toilet will not burp until you reach the level of the vent pipe in the tank. This may be the way to tell if the vent pipe has extended into the tank to far. I would monitor each flush from an empty tank until I get to the point that the toilet will burp the air back out the toilet.
If the pipe has extended into the tank you will be looking at a not easy type of repair.
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Old 08-13-2022, 08:31 AM   #13
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blocked vent or tank is full

check the vent ... get on top and check for any wasps nests etc
have someone dump 5 gallon bucket into toilet and see/hear/feel if air is venting

some people more sensitive to the odor..
it may be functioning properly but some smell when flushing is inevitable ...

give everything a thorough cleaning... empty the tank flush it with hose down the bowl if no flush tube ... fill it 1/2 to 3/4 full and add some of your favorite stuff to loosen and dissolve waste. then take trailer for a longish drive to slosh it around.
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Old 08-13-2022, 08:36 AM   #14
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Just a couple of guesses here. Do you have an unused washer drain that's not blocked off? You had "professionals" clean the black tank? You should be able to go four or more days with just two people, leading me to think there are still solids in there. I'd try using a Swivel Stick to break up anything left behind in the black tank.
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Old 08-13-2022, 09:16 AM   #15
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As a matter of fact, this trailer did have the washer installed but removed by previous occupants. Will have to dig around and see what they did. The smell doesn't come from the bathroom area, it just suddenly appears everywhere at once.
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Old 08-13-2022, 10:23 AM   #16
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Sewer Gas

If the toilet is a Dometic 300 those are noted to leak and collect waste between the bowl and inside the base. The solution is to replace it with a Dometic 310. Contacting Dometic may get a free replacement. They know there is a problem with the 300 toilets.

I tried unsuccessfully to repair our Dometic 300. The final solution was to remove it and throw it in the trash. I then purchased a Dometic 310 which has a porcelain bowl. A much nicer toilet and doesn't leak or smell. I understand the 320 is even nicer.

Bob
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Old 08-13-2022, 11:34 AM   #17
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I was getting a smell in my Rig and upon inspection of the unused washing machine hook I found the drain has a “mechanical trap@ meaning it’s just a flapper on a spring. It was stuck open and the smell permeated the screw in cap on the waste line.
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Old 08-13-2022, 11:37 AM   #18
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I Replaced the toilet with a new 320. Toilet is one of the few places that doesn't have the gas problem.
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Old 08-13-2022, 11:40 AM   #19
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There is a washer drain pipe but it has a plug in the end. Can't find an air valve anywhere as the plumbing is almost entirely in inaccessible locations.
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Old 08-13-2022, 08:17 PM   #20
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any chance the smell is gray water?
just went to my trailer been sitting for a while...

the water in the P trap had evaporated enough to make the trailer stinky
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