We are living in a Park Model (small mobile home).through the months of May & Oct.
The house is not on a foundation, and has skirting all the way around.
We are getting a smell under the bathroom sink. The house does not have exterior venting.The sink & toilet drain into a holding tank that gets dumped every 6/7 days.
When we first started living in the house we did not have a problem but now we do.
It is a extremely obnoxious smell, similar to a mixture of ammonia and urine.


I was wondering if I could just cap this pipe without doing damage to anything else.

I do not have a way to vent to the roof without major construction.

Check the trap for that sink to see if it is holding water. Lacking a vent the trap may be getting siphoned and without water it will allow sewer gas into the home. Drop the trap straight down with a bucket under the trap. The trap should be full of water to the point of overflowing on the short side.

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I was wondering if I could just cap this pipe without doing damage to anything else. I do not have a way to vent to the roof without major construction.

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I wouldn't cap off the drain but I would install a AAV,(Air Admittance Vent) just downstream from the trap, (see image) and see if venting the lavatory doesn't help. Good luck, Tom