Gray tank smell 💩when ac is on

[Rikadoo]

OK SO THE WIFE AN I NO LONGER JOKE ABOUT “who cut one”😳💩 last season i found out what i belived to be the air diverter valve under the sink, it was over 100 outside, an 75 inside, the first day was awsome... after that, not so much, in fact it was DISGUSTING!!!

After dumping the gray tank it still had hang time but it took getting to cooler ambient temps for it to quit. So i replaced both valves an thought it was done, in fact i took a trip in Feb to Quartsite an no problem, however I never had to use the air conditioning. Now I’m in a place where is the temperature outside is 90° so I got into the coach and turn on the AC and immediately was reunited with that stink, I then opened all the windows turned off the air conditioning and now the smell is gone how is the air conditioning bringing the smell from the gray tank into the coach??? Last fall i washed, rinsed, filled the tank with water an happy camper. It seems to ONLY happen hot outside with the ac on, it appears to be coming from under the kitchen sink!!!

i thought it had to do with negitive air pressure from the ac systems causing a SUCK to pull the air in from the gray tank. I have concidered the roof jack vent is getting air blowing from the front condencer fan pushing air towards it, then i relised i had 4 beers an that was crazy thinking. So now with the AC off its doing just fine...

I had been away from the rv for 4 days, i poured water in each drain, the washer cabnit still has the pipe capped so no draft! 
 I suspect the the cold air inside is drawing air from the hot gray tank, im just unsure how to stop it, thinking need a air diverter valve with a tighter seal but???? 
 

[Dr4Film]

My coach has FOUR mechanical air vent valves not two, one under the kitchen sink, one under each bathroom vanity and one in back of the Spendide Washer/Dryer.

Perhaps you have missed one or two depending on the floor-plan of your coach.

Plus I did not purchase the cheapo mechanical air vents but rather the more expensive ones so I wouldn't have to do it again and again.

I find that when I have the coach parked under our winter home and run the AC's daily, upon entering the coach you can smell the grey or black tanks at times. That is because the AC's usually remove the water in one or more of the drains. So I have to go through and make sure that ALL of the drains are full and then keep them that way. So every so often I run water into all of the drains plus run water into the washer dryer then spin it out.

After doing all of that the smell always dissipates.

Had that problem while wintering in Florida this year when the hot weather returned but after going through my routine the stench was gone.

One last thing I found never to do when in Florida is to have any strong rooftop fans going when the toilet valve opens otherwise the fans will pull the air from the tank into the coach especially the one in the toilet room.

[96 EVO]

Can't see why running the AC causes this. All it does is cycle the existing interior air!

Doesn't remove any, doesn't add any.

[Rikadoo]

So another question is what type of drain valve is in the shower, does it require maintance? An thank you for the info of the washer drain pipe having a vent valve i will check for that. As for the valves i bought the cheaper ones ONLY cause i thought that if they lasted since 03, then like models would be just as good... im going to change that! Im glad this is happening now so HOPEFULLY i can get it fixed in time to head out to the desert, thanks Richard iwill keep everyone up on the progress

[Guest Ray Davis]

Rik,  are we talking about a roof AC or the dash AC?

Maybe the foul smell is coming from the AC itself.   What does it smell like?

[Scott 61]

Just a shot in the dark make sure your washing machine drain hose is not too far down in the drain pipe it will push all the water out of the P-trap

[Dr4Film]

My shower has a p-trap for a drain as does all of the sinks and washer/dryer.

[Hypoxia]

27 minutes ago, Ray Davis said:

Rik,  are we talking about a roof AC or the dash AC?

Maybe the foul smell is coming from the AC itself.   What does it smell like?

I was wondering if the evaporator is clean or if it has fermongoloids growing on it?

Assuming each P trap has water in it, shower included, that side of the system can't leak.  An air vent valve can go bad especially in the desert heat and is there a possibility you missed one?  I would have expected 3 or 4.  You could cover them with saran wrap or similar for a test run.  A duct leak to the exterior could cause negative pressure but so does a roof vent fan. 

[6Wheels]

We experienced the odor when underway.  By keeping all openings closed and running the A/C or heat it dissipates after about 30 minutes.

After about 5 years the original mechanical vents (sink, toilet, shower, washer) had to be replaced.  We upgraded to HepvO traps where we could (replaces P-trap) so water is no longer required to isolate the smells.  Couldn't get to the shower drain or the washer.  One way to fix the washer is to run a vent pipe to the outside if not already done.  The shower is another story and of course is usually the one that has the problem.  Ours is right in the bedroom of course.  We removed the electrical panel which is in front of the vent and installed a vent on the outside wall (don't hit the frame!).  Fixed it.

[Rikadoo]

Yeah right now im parked out behind a shop, im trading labor. Im rewiring a friends 48 Ford, an hes removing my leaking radiator, i took the radiator to a radiator repair shop an they said they cant fix it due to being aluminum an it failed because of Electrolysis an that it will fail again. So today im ordering one from Source.

Anyway that said im sitting in a wide open space with sun directly on the passenger side, im running the house air. I like the saran wrap over the valve to do some diagnostics. Yesterday morning i had the door shut with the vent fans on an it was stinking, i open the door an the smell went away.

In addition and to be fair my gray tank is 3/4 full, once i conclude the diagnosics of wrapping the valve then turn on the ac if the smell is gone im callin the honey wagon to get pumped out, i would have thought the level of the tank shouldnt make any difference. 

[96 EVO]

44 minutes ago, Rikadoo said:

  i would have thought the level of the tank shouldnt make any difference. 

Shouldn't, unless the tank vent pipe was either installed too deep into the tank, or has come loose, and slipped down deeper into the tank.