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Old 07-23-2023, 02:00 PM   #1
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Odor under bed from black tank

Puma 31-RLQS 2018 w/ enclosed underbelly, purchased new.
Our camper is parked at our hunting camp; we donít move it. We use it on weekends for two night stays. We do not use the toilet for solid waste, and when we get ready to leave we drain the black tank, back flush, drain again, then add some clean water with a little deodorizer to keep it from sitting dry while weíre gone. If we donít do this the smell is horrible when we get back.
By the second evening, odor wafts in from under our bed every time the toilet is flushed. The black tank is not situated under the bedroom, the odor doesnít come in from the toilet, but very strong from under the bed, and thereís not enough time for the tank to get very full before the odor starts. The drain valve is closed and doesnít leak, the roof vents are clear, and there are no leaks anywhere else or it would have ruined the underbelly cover by now. For the life of me I canít figure out how the odor goes into the bedroom under the bed so bad when the toilet is flushed and the odor isnít as bad in the bathroom, especially when thereís nothing under the bedroom. If we leave it be until we do our normal cleaning routine before we leave, the odor begins permeating the camper and also outside. Anyone else experience this? Is there a fix? Do we simply have a defective tank that we canít do anything about?
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Old 07-23-2023, 03:21 PM   #2
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Odors are hard to trace. They can get into the framework and come out at odd places.

I assume you have have sewer hookup since you flush your tank. Try just hooking up the flush and letting it run until the water runs clear. This may take 15-20 minutes. I think of you do that and then backfil you will find that the water comes out pretty clear. Iíve had an RV since 2013 and just recently discovered that just letting it flush until clear removed all the black water. Try itÖ run until clear and then back flush and see how clear the water is coming out of the tank.

You never mentioned your gray water? Gray water and sewer water are hard to distinguish between. Have you replaced you air admittance valves lately? I had one bad in the bathroom sink and the odor (smelled like sewer) came out of return vent for the furnace in the kitchen. You should have one under sink in bathroom and sink in kitchen.

My 2 cents worthÖ
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Old 07-23-2023, 04:53 PM   #3
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If the above doesn't help, you might have a leak in that black water pipe from the toilet to the tank. Your toilet is right next to the bedroom slide so it would be easy for water to run from the toilet to the bedroom.

Under our shower we had a leak where the grey water pipe had become disconnected. There's an access panel near the floor at the front of the shower on ours. The person who repaired it for us found that the black water pipe from the toilet to the tank ran under the shower and was loose. Luckily it hadn't become detached.

One other possibility is that the plastic seal under the toilet (similar to the wax ring in residential toilets) has deteriorated and black water is seeping under the bed. The plastic rings are pretty flimsy and are easily replaced.
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Old 07-23-2023, 05:08 PM   #4
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Thanks for the possible areas to check. Iíve checked for water leaks. This has been an ongoing issue since we bought the camper, so if it actual water leaking from the black tank it should be noticeable somewhere. The enclosed underbelly is a blessing and a curse, but if there were water coming out underneath somewhere it would have damaged the underbelly cover and there is no damage. Itís really like flushing the toilet disturbed the water and the fumes waft out, but why from right underneath the head of the bed is beyond me. We have two valves on the black tank for the drain so it isnít a matter of black water getting into the drain line. And for the little time weíre here you wouldnít think thereís be enough in the tank to smell so bad. I do rinse out and fill with Dawn and water softener to clean it out, but it really doesnít solve the issue of the fumes once weíve been here for a day.
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Old 07-23-2023, 05:48 PM   #5
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What kind of toilet do you have? The Dometic 300 is notorious for retaining 'stuff' within the tank. Shouldn't result in fumes under the bed though.
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Old 07-23-2023, 06:48 PM   #6
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What kind of toilet do you have? The Dometic 300 is notorious for retaining 'stuff' within the tank. Shouldn't result in fumes under the bed though.
Iím not sure toilet brand but everything in the camper is the absolute cheapest possible so Iím betting it is. But like you said, doesnít explain fumes wafting up under the bed when the water in the tank is disturbed. I just filled the tank with clean water, Sawn and some Calgon to let it sit till we get back in a few days. Wonít stop the ongoing fumes issue but hopefully will help. Iím almost tempted to take the drain pipe off that runs to the washing machine hook up. Thatís the only thing that ties into the system that runs under the bed slide out.
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Old 07-23-2023, 06:55 PM   #7
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Washing machine drain

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Iím not sure toilet brand but everything in the camper is the absolute cheapest possible so Iím betting it is. But like you said, doesnít explain fumes wafting up under the bed when the water in the tank is disturbed. I just filled the tank with clean water, Sawn and some Calgon to let it sit till we get back in a few days. Wonít stop the ongoing fumes issue but hopefully will help. Iím almost tempted to take the drain pipe off that runs to the washing machine hook up. Thatís the only thing that ties into the system that runs under the bed slide out.
The washing machine likely drains to a gray tank, not the black tank. But gray tanks can stink, too.
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Old 07-23-2023, 09:32 PM   #8
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As dalford said in post #2 above odors can be tough to trace. If its not the toilet or a leak below the toilet, its possible it could be a faulty air admittance valve located under one of the sinks.
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Old 07-23-2023, 11:05 PM   #9
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Iím not sure toilet brand but everything in the camper is the absolute cheapest possible so Iím betting it is. But like you said, doesnít explain fumes wafting up under the bed when the water in the tank is disturbed. I just filled the tank with clean water, Sawn and some Calgon to let it sit till we get back in a few days. Wonít stop the ongoing fumes issue but hopefully will help. Iím almost tempted to take the drain pipe off that runs to the washing machine hook up. Thatís the only thing that ties into the system that runs under the bed slide out.
One sure way to know if it is your toilet is the type of smell. If the smell is a heavy urine smell, like a dirty menís bathroom, then it most likely is the toilet. The Dometic Model 300cis famous for that. Search it on this forum.
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Old 07-24-2023, 08:51 AM   #10
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As dalford said in post #2 above odors can be tough to trace. If its not the toilet or a leak below the toilet, its possible it could be a faulty air admittance valve located under one of the sinks.
That is great info. Itís not the grey tank, but I can double check to see if thereís one thatís effecting the toilet.
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Old 07-24-2023, 08:56 AM   #11
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One sure way to know if it is your toilet is the type of smell. If the smell is a heavy urine smell, like a dirty menís bathroom, then it most likely is the toilet. The Dometic Model 300cis famous for that. Search it on this forum.

It is definitely the toilet. When the tank first starts smelling when the toilet is flushed and the disturbs the water in the black tank, the fumes waft in from under the bed, but eventually weíll start smelling it at the toilet when we flush too. It just doesnít make sense that the odor comes in from under the head of the bead. Iím wondering now if the tank has a bad seal and because of the underbelly cover the fume get trapped under the camper where we can smell it from under the bed. No way to check without destroying my underbelly cover 😔
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Old 07-24-2023, 08:59 AM   #12
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The washer drain ties straight in to where the black tank drain valve is, not that it goes to the black tank just that the drain pipe runs along under the slide out where the head of the bed is. The valve stays closed but I’m wondering if that pipe is somehow the culprit for carrying the fumes that we smell under the bed.
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Old 07-24-2023, 09:13 AM   #13
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Can you check the black tank vent pipe?. They have been known to come loose on occasion.

Just a thought / guess.

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Old 07-24-2023, 09:25 AM   #14
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I’ve been on the roof to check the vent pipe and all looks fine.
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Old 07-24-2023, 12:55 PM   #15
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I wonder if there shouldn't have been a U trap on that washer drain line to prevent fumes coming up.

But the real question is DO YOU HAVE THE BLACK TANK DRAIN VALVE OPEN ALL THE TIME? Never do this. Solid waste will build up in a pile in the tank. Leave that valve closed until the tank is full.
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Old 07-24-2023, 01:50 PM   #16
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EAnn.. I just looked up your RV layout and can see the toilet is sitting next to the bedroom wall. I also see you bed is a slide and you say the smell comes from the head of your bed. It must come up into the box your bed is built on then works its way to the head since the slide would be out?

Can you lift the foot of the bed? Mine lifts and is on pistons. If you lift it can you smell the odor?

I’m assuming you black tank is pretty direct under your toilet. Not sure if it is mounted forward toward bedroom or back or where.

I know you don’t want to and have put it off but it seems you need to get under the trailer and remove the coroplast to see what may be going on. It seems you should be able to remove it without destroying it. Anyone else on here ever removed and replaced the bottom cover on this unit?

Even when you do get under the unit it will be hard to see what is going on because all the connections will be on top.

Get a snake camera first. They are cheap…
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Old 07-24-2023, 02:36 PM   #17
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The bed frame is mounted to the floor with subfloor that’s slide in and out with the slide out, so I can’t lift anything to see underneath. I haven’t lifted the mattress to smell under the bed since the odor is so prominent even without lifting the bed. It just seems to me that with a closed tank, if any steel has built up the first place the odor would start coming in from would be the toilet. For the odor to be detectable from outside the tank as water from the toilet disturbs the water in the tank doesn’t add up.
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Old 07-24-2023, 02:40 PM   #18
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Quote:
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I wonder if there shouldn't have been a U trap on that washer drain line to prevent fumes coming up.

But the real question is DO YOU HAVE THE BLACK TANK DRAIN VALVE OPEN ALL THE TIME? Never do this. Solid waste will build up in a pile in the tank. Leave that valve closed until the tank is full.
There are two valves that empty from the black tank and they both stay closed until we need to drain the tank. If the back valve were to be open, contents from the tank would flow to where the other valve is closed, which would defiantly allow an odor issue, but Iíve thought to check this and the valve is closed when the odor inside the bedroom is detected.
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