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Old 05-16-2022, 09:23 AM   #1
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Black Tank Odor

We bought our Class C in December of 2020 and take it out about once a month all year long (we live in Texas). However, we are having issues with our black tank odor. We use Happy Camper, LOTS of water, and flush the tank 3-4 times every time we dump, then load it back up with water and Happy Camper. When we pick it up from storage, it's fine. After one day of use, it smells like an outhouse - no matter what we do. We've checked the vent, by sending water from the roof, and it lands in the tank with no visible leaks. I'm at a loss as to the problem, and we are taking a three week trip in July. I can't live with an outhouse smell for 3 weeks.
Any suggestions about what I could be missing? Or another way to check the vent? I'm afraid that it is venting into the bathroom, but I thought our trouble-shooting measure proved the vent was functional. Help and advice would be so welcomed.
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Old 05-16-2022, 09:52 AM   #2
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Hmm this is a tough one because you hit most of the points.

So since you hit all the main points, I will share my out lier personal experience.

At one particular campground, we went there maybe 5 times a year. I would dump doing my normal process. After camping there, we would have a bad stench within a week or two every time.
Turns out the only dump lane in the campground is tilted away from the waste valve side. So it wouldn't dump all the way. I decided to put down my hydraulic stands on the passenger side and a lot more crude came out. Never had that issue again there.
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Old 05-16-2022, 10:00 AM   #3
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2 things come to mind, the seal at the bottom of the toilet or air pressure in the black tank while driving due to roof vent design. Ours had a similar issue although after 3-4 days, not just 1 day like yours. It always showed up while driving. I had a new toilet and the floor seal was good so I knew that wasn't the problem so I ordered 2 of these https://www.amazon.com/Lippert-Compo...74999996&psc=1 and after installing them we no longer have the issue. Instead of letting air pressure into your tanks it siphons air out for a negative pressure so odors can't escape into the rig. I know everyone says it shouldn't matter if everything is sealed properly but in our case it did matter, and this worked.
Another thing I did was fill the black tank while in storage with Dawn dish soap and water, left it for over a month then drained. I was surprised at the amount of "brown" that came out.
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Old 05-16-2022, 10:04 AM   #4
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I suspect you may have a faulty air admittance valve. check underneath your sink in the bathroom for an air admittance valve. That’s what gave me the smell in our rv, even though I religiously rinse the black tank after each draining. The valve is usually black and sits on top of a vertical pvc pipe. You can buy one at lowes or Home Depot for under $9. Hope that resolves your issue.
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Old 05-16-2022, 10:12 AM   #5
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Waste tank odors inside RV.......

Does Toilet bowl hold water?
Water is a vapor barrier

Can you smell stank at base of toilet?
Toilet floor flange old/not sealing

Do you have a washing machine?
Dry 'P' trap allowing waste tank smell back into RV

Sinks/shower 'P' traps dry?
Waste tank smells back into RV

Air Admittance Valves on Sink drain Lines (kitchen/bath) not closing
Should only open when draining then close. If they fail to close waste tank smells back into RV

GREY tanks can SMELL worst then Black tank....rotten food bits, rancid grease/oils, urine (come on folks pee in shower), slough skin cells, hair etc

I bet the Air Admittance Valve under Bathroom sink is staying open
Put plastic bag over it, seal with tape and see if smell goes away
AAV's are just hand screwed into stub downstream of 'P' trap. Easy to replace....available at Hardware Stores


*****Warhorse6 types faster and isn't as long winded as me but I agree with him
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Old 05-16-2022, 10:20 AM   #6
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https://www.lowes.com/pd/Keeney-Plas...-Valve/1069119

Here's a link for air admittance valve that I used as a replacement in our rig, and we were having a problem with sewer odors in the bathroom and adjacent area. I also went ahead and replaced the one under the kitchen sink.
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Old 05-16-2022, 10:29 AM   #7
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Quote:
Originally Posted by Warhorse6 View Post
I suspect you may have a faulty air admittance valve. check underneath your sink in the bathroom for an air admittance valve. Thatís what gave me the smell in our rv, even though I religiously rinse the black tank after each draining. The valve is usually black and sits on top of a vertical pvc pipe. You can buy one at lowes or Home Depot for under $9. Hope that resolves your issue.
Good point, I forgot that some RV bath sinks drain into the black tank which was not the case with mine.
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Old 05-16-2022, 10:33 AM   #8
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Great suggestions

Quote:
Originally Posted by Old-Biscuit View Post
Waste tank odors inside RV.......

Does Toilet bowl hold water?
Water is a vapor barrier

Can you smell stank at base of toilet?
Toilet floor flange old/not sealing

Do you have a washing machine?
Dry 'P' trap allowing waste tank smell back into RV

Sinks/shower 'P' traps dry?
Waste tank smells back into RV

Air Admittance Valves on Sink drain Lines (kitchen/bath) not closing
Should only open when draining then close. If they fail to close waste tank smells back into RV

GREY tanks can SMELL worst then Black tank....rotten food bits, rancid grease/oils, urine (come on folks pee in shower), slough skin cells, hair etc

I bet the Air Admittance Valve under Bathroom sink is staying open
Put plastic bag over it, seal with tape and see if smell goes away
AAV's are just hand screwed into stub downstream of 'P' trap. Easy to replace....available at Hardware Stores


*****Warhorse6 types faster and isn't as long winded as me but I agree with him
The toilet does hold water. I've even put diluted colored cleaner it to see if it leaked out. It held.

We will check the seal at the base of the toilet - we may need to remove it. It's a Dometic toilet.

No washing machine, but we've treated the gray tank as well and make sure to have water in the P traps - it is definitely the black tank.

We can't seem to locate air admittance valves under the bathroom or kitchen sinks. We've removed the panels and only see the water lines and the drain pipe.
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Old 05-16-2022, 10:34 AM   #9
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No valve

Quote:
Originally Posted by bigb56 View Post
Good point, I forgot that some RV bath sinks drain into the black tank which was not the case with mine.
We can't seem to locate an air admittance valve under the bathroom or kitchen sinks. We've removed all panels and only see the water lines and drain pipes.
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Old 05-16-2022, 11:10 AM   #10
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Siphon vents

Quote:
Originally Posted by bigb56 View Post
2 things come to mind, the seal at the bottom of the toilet or air pressure in the black tank while driving due to roof vent design. Ours had a similar issue although after 3-4 days, not just 1 day like yours. It always showed up while driving. I had a new toilet and the floor seal was good so I knew that wasn't the problem so I ordered 2 of these https://www.amazon.com/Lippert-Compo...74999996&psc=1 and after installing them we no longer have the issue. Instead of letting air pressure into your tanks it siphons air out for a negative pressure so odors can't escape into the rig. I know everyone says it shouldn't matter if everything is sealed properly but in our case it did matter, and this worked.
Another thing I did was fill the black tank while in storage with Dawn dish soap and water, left it for over a month then drained. I was surprised at the amount of "brown" that came out.
This vent sounds like an easy thing to try - thank you!
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Old 05-16-2022, 11:18 AM   #11
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Quote:
Originally Posted by tdelong View Post
We can't seem to locate an air admittance valve under the bathroom or kitchen sinks. We've removed all panels and only see the water lines and drain pipes.
AAVs.....installed after 'P' trap on vertical stub before drain line turns downward








Have you checked your BATTERIES
Boiling batteries form overcharging can STINK
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Old 05-16-2022, 11:19 AM   #12
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Follow the drain from the bathroom sink. It should run to the p trap and to the drain pipe. If it turns upward first, at the top of that line would be the air admittance valve (if you have one.

One other think, if you don't have a p trap, then you have aself sealing waste valve
https://www.rvupgradestore.com/Hepvo...xoCAmUQAvD_BwE

It is just a rubber diaphragm that opens while draining and closes again. If you have that sort of drain, make sure it closes.

There is also a swivel vent for the roof that worked for me after trying everything else. https://www.amazon.com/Camco-40595-W...41475026&psc=1
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Old 05-16-2022, 11:31 AM   #13
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An air admittance valve can hide pretty well up behind a sink. On ours, it's hidden but the giveaway for it is a "T" located on the discharge side of the P-trap. The aav is on the pipe running up from the T.

As far as smell, there are many times when gray water stinks more than the black water.
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Old 05-16-2022, 11:41 AM   #14
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No vent

Quote:
Originally Posted by Old-Biscuit View Post
AAVs.....installed after 'P' trap on vertical stub before drain line turns downward








Have you checked your BATTERIES
Boiling batteries form overcharging can STINK
The batteries are fine.
There is no vent under the sink. Just the regular drain pipe.
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