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Topic ClosedSewer Vent - Event Date: 05 Dec 2017 - 06 Dec 2017
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Calendar Event: Sewer Vent
    Posted: 12 Aug 2020 at 1:11pm
Originally posted by StephenH



One other thing--don't run the vent fan when you flush. It will pull stinky air from the black water tank since there is a straight shot to the tank and no trap. That is the same as the traps in the sink and shower. The fan will pull stinky air from them if you don't have enough windows open. It will pull from the source with the least resistance.

Good point on the toilet ball valve. That could conceivably leak stinky air and cause a smell since there is no water seal, although I haven't seen any reports of that on rpods. The swivel roof vent might arguably help with that but personally I'd rather replace the ball valve if that happened so there was a good seal there. 

As for the ceiling fan drawing air through the traps, I assume you mean if they are dry. There is no way that little fan can produce enough pressure differential to displace a couple inch water column in a trap. A hurricane won't even do that. 
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Posts: 6285 		Direct Link To This Post Posted: 12 Aug 2020 at 1:19pm
The issue is not the valve itself. It is that the valve is a plate that slides open to flush. When that happens, there is a straight (or almost straight in the case of our 179) shot from the toilet bowl to the sewage tank. That is why running the fan can pull stinky air from it. When it is closed, it is sealed and normally has at least some water covering it. When that is the case, if the fan is running and there are ot enough other sources of air, the negative pressure will pull stinky air through the gray water plumbing if the traps are not full. I don't think that the vacuum breakers behind the kitchen sink and bathroom sink would contribute to that unless one of them is defective and not closing properly. That would also be something to check as would the check valve/vacuum breaker for the black tank flush. If that check valve is installed backwards, it could allow stinky air from the tank into the area of the valve if the vent fan is creating too much negative pressure.
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offgrid View Drop Down
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Posts: 5290 		Direct Link To This Post Posted: 12 Aug 2020 at 1:43pm
Originally posted by StephenH

The issue is not the valve itself. It is that the valve is a plate that slides open to flush. When that happens, there is a straight (or almost straight in the case of our 179) shot from the toilet bowl to the sewage tank. That is why running the fan can pull stinky air from it. When it is closed, it is sealed and normally has at least some water covering it. When that is the case, if the fan is running and there are ot enough other sources of air, the negative pressure will pull stinky air through the gray water plumbing if the traps are not full. I don't think that the vacuum breakers behind the kitchen sink and bathroom sink would contribute to that unless one of them is defective and not closing properly. That would also be something to check as would the check valve/vacuum breaker for the black tank flush. If that check valve is installed backwards, it could allow stinky air from the tank into the area of the valve if the vent fan is creating too much negative pressure.

We agree that the traps would have to be dry for the fantastic fan to pull air up that way.

I got that you can get stinkies for the few seconds the ball valve is open. If the valve itself were to leak air (which is possible but I haven't heard of it) then that would be a continuing source until fixed unless the black tank is kept at negative pressure relative to the bathroom, which the roof swivel vent would presumably help do. A faulty black tank flush valve could conceivably cause an issue. In either case, I'd rather smell it so I know to go fix it than have a swivel vent concealing the problem. 
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Posts: 6285 		Direct Link To This Post Posted: 12 Aug 2020 at 1:47pm
One other consideration is the seal between the toilet and the floor. 'm not sure if there is something like a wax ring there. If that is not sealing properly, stink could be pulled through there.
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Posts: 14 		Direct Link To This Post Posted: 13 Aug 2020 at 3:36pm
Great points everyone. I'm adding this as a best practice for the family when using the bath.
- Dry everything after a shower (already doing that out of pure perfectionism.)
- Cut the fan before flushing if no windows are open.
- Generally try to have windows/door open if the fan is pulling.

The description of where the fan is going to pull its air from is illuminating. I had not considered all the places it could potentially be pulling from and what that might do in terms of smells.

In any case, not gonna replace that vent anytime soon. We'll just enjoy things until a problem arises.
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