Plumbing Vent

[KimberDon]

My question has to do with the black water tank vent. Our 2011 Montana 5th had a broken vent cap when we bought it last year, which I immediately replaced, but we have a persistent odor in the basement compartment and often inside the trailer. Looking down into the vent pipe with a flashlight doesn’t show an obstruction, but it’s hard to see well. I’ve tried lowering a garden hose into the pipe and hooking a vacuum to it, without results. My question is, would flushing with a water spray go directly into the tank, or is there a valve that would prevent the water and any obstruction from being flushed into the tank.

[JRTJH]

Depending on the location of the black tank rooftop vent and the location of the 14" roof vents, the direction of the wind (or air conditioner exhaust) can direct the "black tank odor" toward the open roof vents. If the exhaust vent has a powered fan and it's turned on, it may actually "pull black tank odor" through the toilet while flushing. If there's any damage to the cap, or if it's pushed too far down onto the vent pipe, it may obstruct the air flow and "could" (not always, but "could) cause pressure to build up in the black tank and could (again, not always) force the odor through the toilet valve and into the trailer interior.

All that said, if you're smelling black tank odors in the pass-through compartment, that is abnormal. There should be no "communication" of any black tank contents with the interior of any storage compartment. I'd suspect a leak, either a cracked pipe or possibly the vent pipe wasn't screwed into the black tank or not glued to the fitting in the black tank. If you have odor in the storage compartments, that needs to be inspected and repaired.

If the odor is caused by "not turning off the fan during flushing"... well, that's on you, and if it's the direction of wind on the roof toward an open roof vent... I'm not sure "who to blame for that".... but closing the vents may help.....

[tech740]

Are you sure it’s the blank tank? I had an air admittance device stick open under the sink. The gray tanks can smell just as bad as black. That would allow the smell into the camper also.

[MerlinB]

Install one of these on top of your vent pipe.

https://www.amazon.com/Lippert-Compo...s%2C155&sr=8-4

[Customer1]

In answer to your question, running water down the vent will go directly into the tank, it should be an open pipe all the way.

The usual suspect for odors is an air admittance valve under a sink somewhere.

[Customer1]

Originally Posted by MerlinB

Install one of these on top of your vent pipe.

https://www.amazon.com/Lippert-Compo...s%2C155&sr=8-4

snake oil

The black tank is a closed system other than the roof vent. Trying to remove air from a closed system doesn't work. Even an electric siphon pump will only create a vacuum, it still won't flow air because there is no inlet.

[flybouy]

If the wind isn't blowing the vent stack odors to an open roof vent and the bathroom fan is off when Flushing then there's one other possibility for vent tank odor. That would be the seal in the toilet valve. The way to check is look in the toilet after it has set overnight. It should still have water in the toilet covering the waste valve.
If all that checks out then start "sniffing" around the gray water system. Many units use Hepvo "waterless traps" for shower and sink drains. They can hold debris or fail allowing tank gasses back into the living space.

[KimberDon]

Thanks for all the feedback and advice. As all vents have been closed and fans off, the under-the-sink valve will be my next checkpoint. I'll likely shoot some water down the vent pipe too, as it was open long enough for leaf debris or insect nesting to be a factor.