Forum Discussion

DaCamper's avatar
DaCamper
Explorer
Aug 01, 2018

Clogged black tank vent stack?

Hey All,

We recently bought a new (used) trailer, 2014 Jayco. I noticed we are having a black tank odor issue, as soon as we flush the toilet we get a strong odor, which quickly goes away after the flush valve shuts and the bathroom airs out. Doesn't matter if the bathroom ceiling vent is on or off. We don't smell a thing as long as the toilet isn't flushed. It is the first time in all my years of camping and 4 different trailers that I have had issues with black tank odors. I did a quick fill and flush (haven't spent a lot of time on that yet), didn't help...I will try a more intensive cleaning. But my sense is it isn't necessarily a fouled up tank. Shining a flashlight down the toilet drain doesn't reveal anything remarkable from the little bit of tank I can see.

I went up on the roof, and took a deep sniff at the black tank vent, and this is my question...If I am having immediate strong odor when opening the toilet tank flush valve, wouldn't it seem to make sense that I should be getting a whiff of the same odor out the roof vent for the black tank? In short, I am wondering if it is possible that the vent stack got blocked somehow. I smell literally nothing at the vent, not even a trace amount of odor. Contrast that to the intense smell I get as soon as I open up the toilet drain/flush.

Just wanted to get some opinions here...I am planning on investigating a bit more, but really curious about not smelling anything at the vent stack.
  • ScottG's avatar
    ScottG
    Nomad
    Aug 01, 2018
    Just about every RV I have checked has had the roof vent installed wrong. They have the black pipe too far up into the cap, which mostly seals it off.
    If you remove the cap and find this, just notch or cut away the black pipe until it is just about even with the white base.

    Also, use tank treatment chems and believe me, it matters if you fan is on. It WILL pull nasty air from the tank inside the rig.
  • pryoclastic's avatar
    pryoclastic
    Explorer
    Aug 01, 2018
    ScottG wrote:
    If you remove the cap and find this, just notch or cut away the black pipe until it is just about even with the white base.
    I'm not an expert but that seems a bit of an extreme default position to take.

    When I replaced the cap on our coach the sewer pipe stuck out of the base but it didn't touch the cap:



    Haven't had any problems.
  • mobeewan's avatar
    mobeewan
    Explorer
    Aug 01, 2018
    If the vent pipe is not blocked there are two other posdibilites. The vent pipe is extending too far into the tank and the contents rise to the point they keep air from going up the pipe and the only place the displaced air can go is into the bathroom or you need more tank treatment. I have had to add more during hot weather on several occasions.
  • rrupert's avatar
    rrupert
    Explorer
    Aug 01, 2018
    I have heard that if you have a vent fan running and the windows and door closed the odors can be sucked from the toilet when flushed.
  • DaCamper's avatar
    DaCamper
    Explorer
    Aug 02, 2018
    Thanks for the advice everyone, I haven't had a chance to check it out yet because the weather isn't cooperating the past couple days, but I will soon.

    We do still get the odor even not running the bathroom fan.

    The RV was in immaculate shape, and seemed well maintained in general. But I have no idea what the tank habits of the previous owners were, so it could in theory be a mess of caked up **** down there. We actually don't use the toilet that much (basically the kids use it at night). This is our last planned weekend of the season, so I will probably give it a hearty flush out the best I can and see what I can do. I am going to get back on the roof, take off the cap, and try to see what is going on.

    I just keep thinking if we get such a strong odor the moment we open that valve, it seems I should smell something out the vent too, at least a trace of it.
  • rrupert's avatar
    rrupert
    Explorer
    Aug 03, 2018
    My dealer friend had a trailer to service and got a mess. The liquids had seeped out of the black tank leaving all the solids behind to set up like concrete. It took a lot of water and time to break things up enough to flow out.
  • campigloo's avatar
    campigloo
    Explorer
    Aug 03, 2018
    If it’s just the vent pipe stopped up, and it very well could be, get up there on a nice hot day. Run a stick or hose down it. If that was the problem you’ll know it once the odor knocks you over. There will absolutely be not a shadow of a doubt.
  • 2edgesword's avatar
    2edgesword
    Explorer
    Aug 03, 2018
    If you not getting any smell from the roof vent then the tube is probably blocked. As for the smell when you flush, if the roof vent is block then some pressure will build inside the black tank and when you flush that pressure is relieved into the RV.

    Take off the vent cover and look down with a flashlight to see if you can see into the black tank. If you really can tell by looking tie something with some weight to it (small enough not to get stuck in the tube) to a string that would be long enough to reach the black tank and see if it will extend that far or if it gets blocked. You could also take a water hose and try running water down the tube. If the tube "quickly" fills with water that would indicate a blocked tube that needs to be unblocked.

    Beyond that ditto what mobeeone said about the tube dropping but the tube would have to drop a few inches for it to be covered by "stuff" that wouldn't allow gas to escape. That amount of drop would probably be evident by little to no tube protruding above the roof.

About Travel Trailer Group

44,029 PostsLatest Activity: Jan 13, 2025