Sewer smell in RV and vacuum question update, comments, and a possible solution

Last week I posted a question from a reader who was having issues with sewer smells and a vacuum when dumping. I got some feedback from the original poster as well as some criticism from DonH. I also got an email just now from another reader who had a similar situation and found the answer. So I thought it was a good idea to post the comments and to provide an update, as most comments are not viewed and a couple of the comments were direct emails that you would not have seen.

Here is the original post.

Here’s the comment from DonH to that post:

Boy, you really missed this one Dave. Read her complaint again: “…so I drain about 50% of the black tank once per week. I’ve noticed lately that when I close the black tank valve during or after dumping, it’s pulling a suction.” Of COURSE it’s pulling a suction – she’s closing the valve with the tank still half full. There’s no way to prevent a suction when you do that because the vent is from the tank, not from the dump line.
The answer is that she should stop dumping just half of her black tank contents. I can’t imagine any earthly reason to do that. Further – the sludge in the tank is in that bottom half (more like bottom 10%) so by doing what she’s doing she’s building it up!

From Mikal H:

Or… It could mean that Kelly dumps the entire black tank contents when it is 50% full.

When I read it I was unclear which it is. Since only dumping half the contents is something I have never heard of, nor can imagine anyone doing, I assumed the tank is around half full when dumped weekly. It does mention closing the valve “during OR AFTER DUMPING” which further confuses which it is…or both!

This is kind of what I thought, as it had just started happening.

This came from Kelly:

Thank you, sir. Ours is the Palomino Sabre 29 CKDS-6 model. I appreciate your response.

Oddly enough, our issue has gotten better since my post. Still monitoring it.

We do have vents in the bath and kitchen cabinets but, not one related to the black tank that I’m aware of.

Thanks again,

Kelly

And this came from Mike, with a 2018 Montana 3720RL:

Replying to Kelly’s problem with the black tank vent problem. I also had somewhat the same problem with our fifth wheel. I discovered through a lot of investigation that the vent pipe had come loose from its mooring and had slipped down inside the black tank. I’ve also had the same symptoms as Kelly described, in her question to you, Dave. I ended up pulling the black tank vent pipe completely out of the tank. I did have to cut the pipe to get the pipe completely out of the tank. Then I used a rubber collar splice with two clamps on it to hold the pipe at the proper level inside the tank, and another collar splice to put the bottom part of the vent pipe back together.

 You might also enjoy this from Dave 

Where are the black tank odors in RV coming from?

Dear Dave,
When I dump my black tank I get an odor in the main living space in my fifth wheel. Do you think the smelly black tank odors are coming through the air conditioner from the vent on top? —Bud

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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