sewage smell in air conditioning after flushing toilet

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Maybe the roof vent opening from your black water tank is close to the roof air conditioner.

They do make a swiveling vent outlet called a Venturi and the air passing by creates a suction but the wind might still be blowing the wrong way.

Welcome to the Forum
 
Any odor when the AC is not running?  I would think the odor is being picked up by the AC return and then blown back into the rig.
 
The line about A/C's sucking in odors or fumes from rooftop.. Does not happen. A/C air is all recirculated.  What is inside is inside what is outside is outside.

Exception: some older units DID have optional fresh air intake or exhaust (Dampers before and after the blower that you could open or close with a control) but nothing I'm aware of made this century.
 
The vent pipe to the roof may have dropped down, or was never long enough, and is venting into the ceiling.  The A/C ducting is often less than perfect allowing air in or blowing out pushing the sewer smell out thru crevices.
 
Another common flaw is the opening where the vent pipe goes through the roof isn't sealed against the side of the vent pipe.  The cover conceals it but the gap can let sewer fumes into the RV ceiling and then they get sucked into the air conditioner's intake.
 
HueyPilotVN said:
Maybe the roof vent opening from your black water tank is close to the roof air conditioner.

They do make a swiveling vent outlet called a Venturi and the air passing by creates a suction but the wind might still be blowing the wrong way.
HueyPilotVN
RV roof A/C units recirculate and cool the inside air ... They do not draw air, (or odors), in from outside the RV.
 
The line about A/C's sucking in odors or fumes from rooftop.. Does not happen. A/C air is all recirculated. What is inside is inside what is outside is outside.

Exception: some older units DID have optional fresh air intake or exhaust (Dampers before and after the blower that you could open or close with a control) but nothing I'm aware of made this century.
Have been dealing with this ever since I bought my 1999 rv. Anytime I flush or drain sewer my ac blows in the nastiest sewer smell in the world. I’ve just dealt with it. But I’m so sick of it. I can go outside on the top and I don’t smell anything. Come back into my room and almost vomit for the thick smell. My 22 year old son can not figure it out. Everyone says it only recirculates the air in the rv. This is absolutly not true. My room did not stink before. The second you flush or pull the drain sewer it’s like it’s draining into my room. I don’t know what to do. I’m ready to trade it in. For a new one. I wish I knew the drain diagram or how the ac hooked up. Bu something somewhere is leaking sewer and I have talked to repair centers and they don’t help at all.
 
Have been dealing with this ever since I bought my 1999 rv. Anytime I flush or drain sewer my ac blows in the nastiest sewer smell in the world. I’ve just dealt with it. But I’m so sick of it. I can go outside on the top and I don’t smell anything. Come back into my room and almost vomit for the thick smell. My 22 year old son can not figure it out. Everyone says it only recirculates the air in the rv. This is absolutly not true. My room did not stink before. The second you flush or pull the drain sewer it’s like it’s draining into my room. I don’t know what to do. I’m ready to trade it in. For a new one. I wish I knew the drain diagram or how the ac hooked up. Bu something somewhere is leaking sewer and I have talked to repair centers and they don’t help at all.
Have you ever taken your inside AC components off your ceiling, and had a look at your ducts?

I'll bet I could fix your problem in a one day review and repair.

How long have you had your 1999 unit?

As I've written in other threads, RV's are mostly constructed with garbage quality care. My AC had the wrong framing piece in the duct work because a lazy worker couldn't be bothered to walk over and get the correct piece. He/she used a framing piece made for the one side that actually routes the air to the main duct. To clarify: That framing piece had the oval cutout intended for attaching ducting. The result was that cold air was being blown into my insulation between my ceiling and roof. It rained in my RV!!! As soon as I covered that cutout and correctly insulated all returns, my problem was solved. The actual duct routing piece was attached, poorly, to my main duct. It is well insulated, and attached properly, now.

I'll bet your ducting and AC framing is a joke, and that your vent pipe has a bad connection in your wall. THAT would be the best explanation for what you're experiencing. You may have to open your wall to check your vent pipe, but don't go there until you check all of your duct work and main AC framing in the ceiling.

Good luck!
 
Everyone says it only recirculates the air in the rv. This is absolutly not true. My room did not stink before. The second you flush or pull the drain sewer it’s like it’s draining into my room.
The AC does not pull air from the outside - as others have stated. So wondering why you state that is absolutely not true?

The room didn't stink before WHAT?

It's seems obvious you have a venting problem. So logically draw out all the vent pipes - the roof vent from the black tank, your AC lines, etc. and determine where something is not connected right. Is your toilet ball valve seal intact? Is there water in the toilet bottom to prevent gases from escaping the black tank? Running an AC can draw out gases if not. Do you leave the toilet cover up allowing water to evaporate?

Do you have the odors if the AC is not running?

Can't immediately think why opening the sewer drain hose would create odors inside as you describe. Could be air entering as tank empties and stirring up the odors.

In the short run, get an enzymatic black tank odor control chemical that will better break down the waste. Yes, yes, posters, many of you are vehemently opposed to this ( I don't understand why), but I swear by my Thetford treatment and won't go without it.

Linda
 
Note that having the bathroom exaust fan running when you flush will suck fumes from the black tank. An air conditioner return could well do the same thing.

Ernie
 
The AC does not pull air from the outside - as others have stated. So wondering why you state that is absolutely not true?
Last weekend, someone's fire smoke was trickling right over my AC unit and it sure did smell up my trailer.
 
Last weekend, someone's fire smoke was trickling right over my AC unit and it sure did smell up my trailer.
RVs are not air tight, so although the A/C itself may not be bringing in outside air, there are many other ways for such smells to get inside. Once a little gets in, the A/C tends to endlessly recirculate it.
 
In the short run, get an enzymatic black tank odor control chemical that will better break down the waste. Yes, yes, posters, many of you are vehemently opposed to this ( I don't understand why), but I swear by my Thetford treatment and won't go without it.
Because it is a waste of money. Pure water works best.
 
It would help to know the unit and layout. Is the location of your ac unit located in the area of the toliet? Do you have duel ac units and one is located next to the entrance door of the toliet?
 
Here is one possibility. The "Stink pipe" as I call the pipe that goes from teh black than THROUGH the roof... might not go through the roof. It might end a few inches short.

And the AC could be sucking air from between the ceiling and the roof...

Suggestion. Pop the top on the stink pipe (remove the "hat" as i call it And inspect if it's short get a short length of black PVC and double male fitting you may need to "shave" a bit off the lower half. .coat it with the proper adheasive and shove it down into the existing pipe to seal. then use a short piece of pool noodle to seal around the part that goes up into the roof pipe.

Not guaranteeing that will help. but it sure can't hurt
 
Have you ever taken your inside AC components off your ceiling, and had a look at your ducts?

I'll bet I could fix your problem in a one day review and repair.

How long have you had your 1999 unit?

As I've written in other threads, RV's are mostly constructed with garbage quality care. My AC had the wrong framing piece in the duct work because a lazy worker couldn't be bothered to walk over and get the correct piece. He/she used a framing piece made for the one side that actually routes the air to the main duct. To clarify: That framing piece had the oval cutout intended for attaching ducting. The result was that cold air was being blown into my insulation between my ceiling and roof. It rained in my RV!!! As soon as I covered that cutout and correctly insulated all returns, my problem was solved. The actual duct routing piece was attached, poorly, to my main duct. It is well insulated, and attached properly, now.

I'll bet your ducting and AC framing is a joke, and that your vent pipe has a bad connection in your wall. THAT would be the best explanation for what you're experiencing. You may have to open your wall to check your vent pipe, but don't go there until you check all of your duct work and main AC framing in the ceiling.

Good luck!
Sir. I am so sorry. I was thinking about something else when I typed that date. It’s actually a 2019 forest river sandpiper 370flok. I bought it brand new from the factory. I had it custom build. Took them about a month and a half and then had it shipped to me here in Texas. But last night I watched several YouTube videos about installing new units and I have a really good idea how it all works now. So I’m planning on next week pulling the unit and looking all around where it was mounted. I have a big ac vent about 3 feet alway from the ac in the ceiling. I’m betting there is something going on there in that space. But I’m going to seal it up real good and hopefully that fixes it. If not then my next course of action it to remove the vent on the roof and add another pipe about 10 feet in the air for venting. The current sewer vent is about a foot and a half from my ac unit. So after I seal the ac really well and raise the sewer vent a little higher I should definitely not have anymore sewer smell in my bedroom. Lol.
 
Sir. I am so sorry. I was thinking about something else when I typed that date. It’s actually a 2019 forest river sandpiper 370flok. I bought it brand new from the factory. I had it custom build. Took them about a month and a half and then had it shipped to me here in Texas. But last night I watched several YouTube videos about installing new units and I have a really good idea how it all works now. So I’m planning on next week pulling the unit and looking all around where it was mounted. I have a big ac vent about 3 feet alway from the ac in the ceiling. I’m betting there is something going on there in that space. But I’m going to seal it up real good and hopefully that fixes it. If not then my next course of action it to remove the vent on the roof and add another pipe about 10 feet in the air for venting. The current sewer vent is about a foot and a half from my ac unit. So after I seal the ac really well and raise the sewer vent a little higher I should definitely not have anymore sewer smell in my bedroom. Lol.
Another thing to consider: Look at the back of your toilet with an inspection mirror, if it's too close to the wall for you to comfortably view. My piece of garbage Dometic 300, has a deep hollow where the water supply connects. Between the top and bottom halves of the unit, there is a seam. What happened in my case was that the sewer smell in my unit was so strong that I was going crazy trying to flush the tank, and use this deodorizer, that deodorizer. Finally, I stuck my head in my toilet! No smell, whatsoever. Then, I caught another horrible whiff. It was coming from the damn hollow, in back of the toilet! The seam was allowing foul water, from flushes, to collect behind the toilet. I took the toilet outside, turned it over, watched it drain, pressure washed the hollow, dried things out, caulked that seam, no trouble after that.

If your AC vent in the bathroom is blowing air against the back wall, it might be forcing the smell from your hollow, if your toilet has one, and stinking up your RV.

If the smell is coming from your main ceiling unit, it's almost certainly what I posted earlier: Bad seals and insulation around your units frame-in and duct work, and a bad connection in your vent pipe, in the wall.
 
Its also possible, when you drain the tank it empties the P-trap in the bathroom sink. That will let the smell come right up thru the sink drain.
As another mentioned, be sure your bathroom vent is closed and fan is off when draining.
 
Have you checked the air-admittance valves in the plumbing? A failed/leaking air-admittance valve can allow sewer odors into the RV when gray tank valves are open. Then you open the black tank drain valve and odors can vent through the plumbing.
 

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