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Topic: Black tank smell, possibly air vent? (Read 643 times) previous topic - next topic
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Black tank smell, possibly air vent?
Hi all! We have been trying to troubleshoot why our rig (2000 MB 26.5) sometimes smells like sewer when we're driving. I noticed that when I fill up our black tank up all the way until I can see the water level coming up the toilet, it starts to leak outside onto the ground.

My wife also noticed that the vent tube that comes up our kitchen countertop looks like it has shifted. I looked at it and it looks a little odd? But seems to be attached. It also looks normal up on the roof.

We notice that sometimes the standing water in the toilet has disappeared, but the behavior is not consistent.

I guess next I should try filling up to 99-100% and check in more detail where the leak comes from? I couldn't locate it when crawling under the vehicle.
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #1 –
If leaks when near full, I would suspect the sewer line from toilet to tank. With tank empty, check for movement at couplings when pressure applied.

Steve
2004 FL
2013 Honda Fit
Re: Black tank smell, possibly air vent?
Reply #2 –
What seems like a black tank odor may actually be from the gray tank. Gray tank food debris can be rather offensive. It may be time to flush that gray tank well and use an odor controller.

The toilet bowl should hold its water if its seal is not damaged. I’ve had the bowl water leak to the black tank in the past. The Mothership recommended spray on table wax to seal the bowl opening. I’ve found that coconut oil does a better job of sealing that type of leak.

Best of luck with your black tank leak.

Kent
2015 27' RB "MissB.Haven"
Re: Black tank smell, possibly air vent?
Reply #3 –
Quote from: kaaeel  - 
Hi all! We have been trying to troubleshoot why our rig (2000 MB 26.5) sometimes smells like sewer when we're driving. I noticed that when I fill up our black tank up all the way until I can see the water level coming up the toilet, it starts to leak outside onto the ground.
My wife also noticed that the vent tube that comes up our kitchen countertop looks like it has shifted. I looked at it and it looks a little odd? But seems to be attached. It also looks normal up on the roof.
We notice that sometimes the standing water in the toilet has disappeared, but the behavior is not consistent.

If the tank is dripping when near full, suspect that the black tank's vent has popped free of the tank and is leaking at that spot when the tank is near full.
The holding tanks are held in by clamps; check to see if both holding tanks are still held up tightly in place.
The gray tanks' vent pipe may also have popped free, it should not move.
There is a possibility that the toilet's floor flange is leaking.


A common cause of toilet leaks is debris buildup in the slide valve, it can be cleaned and lubricated.
If the toilet seal fails, using the manufacturer's repair kit is advised; cheap replacements do not seal well or last long, IMO.

Larry




 

Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Black tank smell, possibly air vent?
Reply #4 –
I have never filled the black tank to "full" until I was filling it with water before dumping.  And I often fill it twice to be sure the sensors are clean.  I can't imagine driving around or sitting in dry camping until the black and gray tanks are both full! That seems creepy to me.  But having lived decades of my life without running water or electricity, even raising children, maybe I'm more picky about sanitation than folks who are used to having modern conveniences.  If it smells... you are doing something wrong.  (BTW I dry camp almost exclusively.)
Kristin from Alaska
1997 MB
Re: Black tank smell, possibly air vent?
Reply #5 –
BTW, my toilet never held water until I had it taken completely apart, cleaned it thoroughly, and all new seals installed.  Presto! Perfect!
Kristin
1997 MB
Re: Black tank smell, possibly air vent?
Reply #6 –
I was of course filling the black tank to full with clean water after rinsing several times.
I had my wife jiggle the black tank vent. I don't think it should be wiggling this much.
https://youtu.be/T-nwSQmRVm8?si=ocph47WK9BGNhqcx

I checked under the vehicle and the three clamps on the black tank look perfect.

The smell definitely seems to be worse with the cover under the sink off, which we have left off for now to troubleshoot.

Next time we're at an RV park with a sewer hookup I'll be able to confirm my suspicion
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #7 –
The vent pipe definitely should not move; this could be the source of your odor problem.
Is it the source of the odor? Well, maybe. Is it the source of the leak? The video shows no signs of leakage at that spot, which I would expect to see.

The holding tank vent pipes' connection to the tank can be made with a threaded fitting, a press-fitting into a rubber coupler, or a glue fitting.
Your vent pipe connection appears to be a loose press-fitting connection, it should not be moving.
I suggest trying a bead of sealant around the spot where the pipes are moving in relation to each other to see if that solves the odor problem.

If the tanks are clean, fill them to the top to see if that helps spot where the leak is coming from.

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Black tank smell, possibly air vent?
Reply #8 –
It almost looks like the pipe has moved up or tank has come down.  Have you looked on the roof if the vent pipe is higher or has same tan distance measuring like at the tank?  Seens that tan portion might need to be further in the tank.  Like that's a sealer of some sort.  Looks like about inch and a half showing.
2000 Mid-Bath
2012 Lance 830 Truck Camper/2006 Cummins Dodge Ram Megacab
1985 Multi Plan - Donated to the American Breast Cancer Foundation.
Re: Black tank smell, possibly air vent?
Reply #9 –
I did look at the tops of the vents and the black tank vent looked about the same as the grey tank one. The view is quite obstructed by the covers though, and the bolts look like they've been on there 25 years and I am worried about trying to take them off tot inspect from the top. But at first glance everything looks OK up there.
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #10 –
I meant to include this image on the original post, it's about 1.5-2 inches shifted up, yes it looks that way to us. And I would agree the tan stuff does look like a sealant that has come loose. I've tried to just shove the pipe down in but that doesn't work I would guess because the alignment isn't perfect and it used to match the diameter of the black tank perfectly and it shifted up and out at some point and now it can't find it's way back in?
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #11 –
Interesting. Are you able to get your phone up to the top of the black tank where the vent pipe enters to snap a photo?
Greg & Victoria
2017 Mid-Bath  “Nocona” towing a manual 2015 Forester
Previously a 1985 TK
SKP #61264
Re: Black tank smell, possibly air vent?
Reply #13 –
Quite likely this unconventional sealant suffered poor adhesion and worked its way up the tube, rather than the tube itself displacing. Rather than pushing it back down, remove it entirely and clean the entire area with isopropyl alcohol, letting it flow liberally down the pipe as necessary. When dry, seal with a new product, such as 3M 5200 fast cure.

Steve
2004 FL
2013 Honda Fit
Re: Black tank smell, possibly air vent?
Reply #14 –
Isopropyl alcohol is a good all-around cleaning solvent, but 3M's datasheet for 5200 adhesive says this:

Limitations:
- Alcohol should not be used in preparation for bonding as it will stop the curing process.
Andy Baird
2021 Ford Ranger towing 2019 Airstream 19CB
Previously: 1985 LD Twin/King "Gertie"; 2003 LD Midbath "Skylark"
Re: Black tank smell, possibly air vent?
Reply #15 –
Excuse my ignorance, but why would liquid be leaking out of an air vent?
Greg & Victoria
2017 Mid-Bath  “Nocona” towing a manual 2015 Forester
Previously a 1985 TK
SKP #61264
Re: Black tank smell, possibly air vent?
Reply #16 –
Quote from: Andy Baird  - 
Isopropyl alcohol is a good all-around cleaning solvent, but 3M's datasheet for 5200 adhesive says this:

Limitations:
- Alcohol should not be used in preparation for bonding as it will stop the curing process.
I suspect this admonition applies to professional rapid repair situations, where time is critical. Done with patience, IPA should dry completely in a short time, leaving no residue that would interfere with curing. My concern is that organic residue might have caused failure of the previous sealant, and using just water will not remove that.

Steve
2004 FL
2013 Honda Fit
Re: Black tank smell, possibly air vent?
Reply #17 –
Liquid was leaking out of the air vent because we filled up the black tank all the way to the top to check where the air would possibly be escaping from. The logic there is if water can escape then air can escape. The water escaping is not really a problem because that only happens when the black tank is filled to the very top. But air escaping into our living area while we are driving is very smelly and that is the problem we are trying to rectify
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #18 –
I don't think I shared a very good screenshot of the air vent above the kitchen cabinet, but it definitely looks like at least the wallpaper covering on the air vent tube has moved up about an equal amount, so that makes me suspicious of the whole tube having moved up. However, when I look at the top of the RV, the covers don't seem to be in a weird place, but there might be enough play for the whole tube to move up and not see anything suspicious on top of the rig with the vent cover hiding any displacement.
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #19 –
Remove the vent cover and see if the tube might have been cut.

Steve
2004 FL
2013 Honda Fit
Re: Black tank smell, possibly air vent?
Reply #20 –
The two holding tank vents are screwed to the roof and cover the the top of the vent pipes. The pipe could move without any visual indication on the roof.
The vent pipe looks like this: the exterior vent covers the pipe where it exits the roof
.https://i.ytimg.com/vi/bVlverXiFAM/maxresdefault.jpg

I would remove the black tank's exterior cap to see what happened and to attempt to push the pipe down into its original position.
I'm still puzzled why liquid would leak without leaving a trace at the loose pipe connection.

Larry
Larry
2003 23.5' Front Lounge, since new.  Previously 1983 22' Front Lounge.
Tow vehicles  2020 Jeep Wrangler Rubicon, 2001 Jeep Cherokee
Photo Collection: Lazy Daze
Re: Black tank smell, possibly air vent?
Reply #21 –
It looks like he jumped up a bit. At some point it looks like someone welded on a new a new screw point for the top cover. Very weird. Why would it jump up?
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #22 –
Hi Kaaeel;  Everything flexes as the vehicle moves down the road. A loose pipe at the bottom, and incrementally every time you hit a bump, it could move up a thousandth of an inch or not. That steel cap has that strap welded for the screw to hold the cap on. Originally the pipe was just above the roof, and that is where it belongs.  Good thing that strap was there to stop the pipe from going up any further. Wouldn't be good to hit a tree branch or anything else.  RonB
RonB (Bostick) living in San Diego
Original owner of "Bluebelle" a '99 TKB
Re: Black tank smell, possibly air vent?
Reply #23 –
We went into an RV repair shop and they had the idea to make a cut into the pipe under the sink to make it easier to work on the lower section of the vent pipe. Hopefully the sealant they used works. They actually accidentally broke the pipe and so had to use a second flexible coupling above the sink. So far no foul odors so I think the sealant works.

Not very pretty though seeing clamps exposed behind the sink but we'll take that over the stench.

Thanks all for help investigating!
Ford 2000 MB
Re: Black tank smell, possibly air vent?
Reply #24 –
We have a point of view on all our projects and repairs which is “if it’s better than it was, then it’s successful.”   Therefore, your repair has been successful.   Well done!