Black tank vent

[Sanford]

We have developed a slight sewer odor on our Challenger. Coming from the cabinet area of the bathroom sink. Upon investigation, I found the cap on the black tank vent loose. I’ve tightened it, but wondered if it was loose for a reason?

[halfprice]

Originally Posted by Sanford

We have developed a slight sewer odor on our Challenger. Coming from the cabinet area of the bathroom sink. Upon investigation, I found the cap on the black tank vent loose. I’ve tightened it, but wondered if it was loose for a reason?

The cap on the roof????

Usually when you get the smell the air admittance value under the sink is bad. You can get a new one at any hardware store like home depot lowes or even Amazon

[Sanford]

The one under the sink. I will probably replace the roof vent too.

[Travelin' Texans]

Originally Posted by Sanford

The one under the sink. I will probably replace the roof vent too.

If you have the air admittance valve under the sink there won't be one on the roof for that sink. The shower drain vent will probably go through the roof as will the toilet. There's most likely that same valve at the kitchen sink so buy & replace both the el cheapo factory ones.
If you have a black tank flush line there's probably a anti siphon valve on that line under the bathroom sink that also goes bad which I'd replace also with a better quality while under there, just be sure to note the direction it's installed so as not to get backwards which will not allow flow.
You can find all these at your local big box hardware store.

[Sanford]

Thanks to all for the help. Off to Lowes I go.