sewer gas odor - trouble shooting

In Tatyana's cabin there is often smell of sewer gas odor. I have checked the potential causes including the sink drain vent (one way) valves and ensure all the u-traps are filled with water. The odor would come and go and is more pronounced if the vehicle is driven with window open, or camping in a breeze.

I am suspecting the sewer gas venting to the vent port on the roof is finding it's way back into the bath room skylight adjacent to it, when the slightest air movement brings it into the skylight which I always leave open for ventilation when the vehicle is parked.

adding this long snorkel ought to fix it

I climbed up to the roof to investigate the vent port. It is located may be 10" away from the bath skylight. I believe sewer gas, which composed of methane is heavier than air and it stands to reason the gas can easily enter the open skylight and enter the cabin.

What's up with the white glove, you ask? I didn't wear because I was afraid to touch the sewer vent for the fear of contracting a terminal disease yet to be discovered by the medical community. You see, my palms are still full of dried skin from excessive amount of boardsailing. Getting to the sewer vent involves erecting a tall ladder and I always wear these nitrile gloves working on any projects hard on the hands. They save your hands and give you much better grip. Next time you see someone picking through the lumber at Home Depot wearing these gloves, it may very well be me.

on the plastic cap it says pull to remove

Fortunately I wasn't stupid enough to just pull to remove as someone before me obviously has done and cause a hairline crack. The small hole is filled with a very tough elastic caulking and I suspect there is a screw below it securing the cap to the main body. Sure enough after I remove the caulking there is a rusty screw. Yep, as expected with most US RV products, suffers from racing to the bottom. They would scrap a penny if they can even if it compromise the longevity of the product. Sure they saved 2 pennies not using a stainless screw.

the cap removed exposing a 1 1/2" ABS pipe

Without removing the ABS pipe, I reach my fingers inside and can feel a spiral vent tube connected to it. With this I now verified the tube did not become dislodged from the vent port.

Actually the first photo with the foot-long snorkel is my evil trick to get you to read the post. It is just a tongue in cheek playful prank.

My test set up is to add a 6" piece of ABS pipe extension. It was late and I didn't want to waste fuel driving to Home Depot. I just tried to find what I have around home to improvise a test setup.
6" extension added

improvised test setup

I am just hoping by elevate the port higher would minimize the gas finding the way into the skylight. I just use duct tape to make the join, which also acts as a breakaway should it hit something. With a 6" extension, it is no higher than the top of the air conditioner.

this is just a version 1 of a prototype - i actually a kind of like the all-business look