Septic smell only when using a/c

[Ralph]

I have Keystone Sprinter 299 ret. The bedroom is in the front next to the bath room. There is roof a/c in the bedroom. We get the septic smell in the bedroom only when the a/c is running and the toilet is flushed. I got on the roof and the black tank vent is right behind the a/c, about 6 inches. I can't believe Keystone didn't think this would cause a problem. Has anyone else had this problem and if so how did you correct it. I'm thinking about putting a 2 foot pvc pipe on the vent to extend it over the a/c. Any ideals ?

[jsmith948]

Your a/c doesn't work like your car a/c.It works like the a/c on your house. It intakes air from inside the rv - cools it and discharges it back into the rv. I think you will find that the sewer smell is being sucked into the bedroom by the return flow to your a/c from the toilet when it is flushed - not from the outside black tank vent. Similar to having the "fart fan" on when flushing.

[Canonman]

Your a/c doesn't work like your car a/c.It works like the a/c on your house. It intakes air from inside the rv - cools it and discharges it back into the rv. I think you will find that the sewer smell is being sucked into the bedroom by the return flow to your a/c from the toilet when it is flushed - not from the outside black tank vent. Similar to having the "fart fan" on when flushing.

This exactly right. Plus, there may be another issue. The Dometic 300 series toilet had a serious design problem. Dometic replaced the toilets with the upgraded 310 toilet and the problem was solved. Worth checking into.
The attached info and pictures are from another RV Forum

"Here's a pic of the source of the odor. This is what a Dometic model 300 looks like when you open up the clamshell style outer housing. You can see the ring of sludge left by the stuff that didn't go through the flush valve into the bw tank.
This is the underside of the Dometic 300 bowl. The opening has an o-ring that is supposed to create a seal at the flange near the flush valve. I believe that this is the source of the leak that is allowing sewage to collect in the inner housing of the toilet. When this sewage sits inside the inner housing for a few days, it creates a foul odor that easily escapes through the opening in the back of the housing."

[Tbos]

How can we tell if we have a Dometic 300 toilet?

[chuckster57]

There is a tag with model and serial number on the back side.

[Ralph]

Thanks everyone. I replaced the black tank vent with a Cyclone and no more smell. Thanks again !!!

[Fwpart]

Howdy folks!

I have the same issue and about drove us to drink this past weekend. Turn on A/C and I can smell the sewage smell through the vents in the Travel Trailer. So much so that we can't stay in the trailer. Ralph, is the Cyclone still working for you? I know that sounds like a dumb question, but see there are other products like Syphon360 and Xtreme Vent and Campco Cyclone. Just wanna make sure that whatever money I invest will actually work. I don't smell anything coming from toilet or sinks, just out of A/C air vents. I figured it was the way the wind blows. I wish I understood the cause a little better so it makes more sense to me.

[Tbos]

I saw a FR brand TT recently and the kitchen sink vent is vented through the side of the TT and out. This would prevent the sewer smell escaping from under sink vents.

[mfifield01]

Does anyone know if they fixed the newer Dometic 300 models? Most of the issues were around 2013. This weekend it seemed to be giving off an odor after less than 2 days. It could've been the Black vent coming in, but I realized I have a Dometic 300.

[Tbos]

Does anyone know if they fixed the newer Dometic 300 models? Most of the issues were around 2013. This weekend it seemed to be giving off an odor after less than 2 days. It could've been the Black vent coming in, but I realized I have a Dometic 300.



I get an odor (sewage smell) when I use the bathroom fan, not while flushing, and I don't have the kitchen vent open. It seems to be pulling the smell from the sink vent in the kitchen. I need to look into replacing that valve. Have not had a problem at any other time.

[mfifield01]

I get an odor (sewage smell) when I use the bathroom fan, not while flushing, and I don't have the kitchen vent open. It seems to be pulling the smell from the sink vent in the kitchen. I need to look into replacing that valve. Have not had a problem at any other time. I noticed a smell in the kitchen area yesterday. I looked under the sink and some type of vent appeared to be loose. It was connected going up off of the sink plumbing. I hand tightened it. I'll see if that helps next time.