Stink from kitchen grey tank

[ice2fire]

We leave a bowl in our kitchen sink. Since the REALLY hot (100F) weather has arrived, we get this awful smell coming from the sink hole drain whenever we lift the bowl away. It's as if the p trap is not working. We have put an "anti-smelly" into the drain, but it has not improved the situation.

This is a used trailer. We note the internal vent (in the cupboard under the sink) has been covered over with a plastic bag. Is this the right thing to do ?

What can we do to improve the situation ? What's happening ?

[DrewE]

ice2fire wrote:
Why does the tank need air going INTO it ? I would have thought that as waste water went INTO the closed tank, air would need displacing.

Physics at work.

The tank itself is vented (open to both directions) to the roof. The air admittance valve is to let the pipe to the tank drain when the water flow from the sink or whatever stops without siphoning the water out of the trap; it's basically a vacuum breaker. It doesn't (or at least shouldn't) let air out because you don't want to have smelly sewer gasses from the tank in your kitchen.

You do need to let air into the tank when dumping the tank. The roof vent is primarily responsible for that.

These are not uncommonly used in normal household plumbing for the same purpose. An alternative is to vent from the traps to the roof vent if that is physically reasonable.

[ice2fire]

Why does the tank need air going INTO it ? I would have thought that as waste water went INTO the closed tank, air would need displacing.

Physics at work.

[ScottG]

My kitchen drain actually has two vents. It has the AAV under the sink which I think is just for using said sink drain and then it has another vent that goes up to the roof. Interestingly, that second vent is hidden in the fridge cavity and just dead ends under the fridges roof vent. I'm sure that second vent is for draining the tank so it doesn't have to pull all that air through AAV - which would probably slow down dumping the tank.

[Old-Biscuit]

rhagfo wrote:

ScottG wrote:

enblethen wrote:
Covering the vent, can allow water in the p trap to be siphoned out.

Good point, where else would the air come from...

So maybe just removing the baggy and/or replacing it will solve the issue.

Yep the water draining to the tank needs that air break after or the trap will be sucked dry. Previous owner likely covered as it wasn't sealing any more.

Exactly.......
Air Admittance Valve.....admits air into drain line to break any vacuum which would suck the water right out of 'P' trap

Putting a plastic bag over AAV is one way of stopping stink from grey tank coming back up thru faulty AAV.
Better way is to replace it.

Also if leaving grey tank drain open cause you have trailer on permanent site.....stink could be due to all the stuff left behind and decaying in the hot temps (sloughed skin, hair, body oils, grease, food particles etc.)
Not being carried out by high liquid level....just trickling out

[daved9664]

quit cookin so much greasy garbage and make healthier meals! 😉

[rhagfo]

ScottG wrote:

enblethen wrote:
Covering the vent, can allow water in the p trap to be siphoned out.

Good point, where else would the air come from...

So maybe just removing the baggy and/or replacing it will solve the issue.

Yep the water draining to the tank needs that air break after or the trap will be sucked dry. Previous owner likely covered as it wasn't sealing any more.

[enblethen]

I doubt whether just removing the bag would help. Previous owner put it on there trying to stop odor, maybe!
We all now the quality of some RV parts!

[ScottG]

enblethen wrote:
Covering the vent, can allow water in the p trap to be siphoned out.

Good point, where else would the air come from...

So maybe just removing the baggy and/or replacing it will solve the issue.

[enblethen]

Covering the vent, can allow water in the p trap to be siphoned out.

[ScottG]

I had that happen once in very hot weather but never again after that. I still dont know why it happened. I too, covered the air admittance valve with a bag in desperation.
I dont know why fumes would get past the P-trap. Maybe it's just the drain pipe leading to it that is dirty. Maybe flush it with super hot water?

Also, if you take the bag off the AAV and odor comes form it, you need to replace it. Home Depot and other such stores have them and they're just a few bucks. linky

[enblethen]

Don't cover it with a plastic bag. Get a new one from any of the larger hardware stores.
The P trap, with water in it, should stop odors from tank coming in through that route.
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