Stuborn odor

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Well-known member
Sep 15, 2005
Southern CA
We just returned from a three day outing in our 2005 Minnie. As usual after I dumped the black and grey water, I added the same chemicals to the holding tanks I have always used. This time however, we now have a persistant sewage odor. It is not coming from the toilet, nor does it seem to be coming from the sink. We have searched the entire rig to be sure there is not a half of sandwich going bad someplace. I seem to remember reading here about a possible venting problem but can not recall the exact circumstances.
Any suggestions ?


I assume you've felt around for any damp places where there was a leak? And looked to make sure that Baby didn't leave you a
"gift" somewhere?
Turns out the shower drain is fine.  Today I open the rig and the smell is still there. A sniff of the sink drains was fine, as was the toilet.
No rotting food either. It really has a sewage smell, and I can not help but think somehow it comes up from the sink area.
I guess my next move will be to fill the holding tank with clear water and fresh chemicals, drive a little and re dump.
What kind of chemicals are you using in your tanks.  Any chemical containing formaldehyde is not really a good thing unless you are trying to preserve the contents of your black water tank.  Also after using formaldehyde products it may take several flushings of the tanks to undo the damage.  Formaldehyde is a great preservative probably one of the best but then why would anyone want to preserve the contents of well  I mentioned it before.  No chemicals is far better than any containing a hyde product.  Many of us here use no chemicals at all and have no odor issues.  If you are going to use chemicals I recommend a product called Pure Power. 

You might try adding about a 1/2 cup of Dawn dishwashing liquid to your tanks fill the tank about half full the take a ride.  Drain and flush tanks a couple times to get the suds out then try using no chemicals at all or if you want add Pure Power per the instructions on the bottle.
Is your toilet retaining a small amount of water after you flush? If not, the ball seal may have something stuck to it (toilet paper?) or is damaged, letting odors come up through it. Also, check all the p-trap fittings under the sinks for any that may be loose and leaking. Check your dump valves for leakage.
Probably the very best thing you can do to take care of the problem is install the rv360 on both the grey and black water vents.  They are powered by the wind and force the odors out the vent pipe.  Best money I ever spent.  Camping World has them as do other places, and installation is quick and easy.
Thanks everyone for you answers.  We never use any "hyde" chemicals. I use any brand that does not have that. I figured since we use our rig once a month that it would be better to have something in the tanks to help with odors. I can see if you full time or use frequently, none would be required.
I'm still puzzled by the odor. I have taken everyone's suggestions as a possible cause to no avial. Next I will look into the vent top from CW.


Clyde, I looked on CW web site for the RV 360. Looks OK but how does it install?  One review talks of using longer screws. Not sure I want to screw into my roof !  How does it install exactly ?


I don't recall seeing an answer to my question about your toilet retaining a small amount of water after flushing. If it doesn't, that could be your only problem - bad, or misaligned seal, or something caught in it. An RV360 needs a breeze to position itself to act as a venturi and create a partial vacuum in the tanks. In calm air it does nothing more than the existing vent. If all drain traps (including the toilet) have water in them, there's no reason for fumes to re-enter the coach except occasionally thru an open window or door. If it takes a partial vacuum to eliminate the odors, that would indicate to me that there is a larger problem such as a crack in one of the tanks, a broken or loose fitting, a poorly mounted toilet, a vent tube that has slipped down into the tank, or something like that. Could even be a clog in the vent pipe such as a mud-dauber nest, or leaves, or any number of other things. Don't waste $25 on something you may not need.
On many (all?) RVs there are vacuum breakers installed on stubs on the drain lines under the sicks.
This opens to allow air to enter if there is  a vacuum that tries to suck the water out of the traps. It has a rubber flap and if it doesn't seal after opening, a sewer odor will hang around under the sink area until it does.

If one needs replacement it is usually pretty easy to do. They screw onto the stub and can usually be removed by hand. Replacements can be found at Home Depot or Lowes.

One other possibility....some toilets have small openings at the top of the bowl under the rim for an overflow. These openings are connected to a tube the runs to the tank. There is supposed to be a low point in the tube to act as a P trap. If this water dries out it can allow odors back into the bathroom.

One more thing to check.

Good luck
Make sure it's not a propane leak!  Sometimes a very small leak can smell like blackwater.  Probably not, but worth a look.  I've always cleaned out the tanks with a little bleach in water.  It's the recommended recharge for tainted well water!
Again, thanks everyone !  I have been out of town for a bit, so the rig had to wait. The toilet area seems to have zero odor I'm really thinking it's a grey water item. I will fill the sinks with enough water to seal the drain, see what happens then.
Anyone have an idea which vent goes to what ? My Minnie has two roof vents ,one on each side. The owners manual does not give this info.


One is directly above the commode in most cases  the other would be the grey vent.
Covered all the drains with water. No change on the odor. Of course gaseous odor would pass through anyway.
This weekend we will have a chance to fill and flush the tanks again. Walmart had the 360 vent for half what CW sells them for so I bought one for the gray water vent. We'll see if that helps.

Problem solved !
I hate to admit the cause, but maybe others can learn from my mistake. I usually shut off all power to the house batteries when parked at home to prevent the slow drain from several items always "on". One of which is the LP gas detector. On this last trip I failed to shut off the LP gas valve at the tank. And as you probably have guessed by now, failed to completely shut off one the stove top gas burners. The smell was LP gas !  Today I turned on the coach batteries in preparation to fill and flush my holding tanks. The LP alarm came on right away. On inspection, I found the one burner slightly on, and of course my LP tank almost on empty. A lesson learned and lucky no harm done or worse.......


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