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Old 10-21-2021, 09:33 AM   #1
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Black tank flushing causes smell in coach

I noticed a smell in my interior the last few times that I have flushed my black tank. When standing outside the coach during the procedure... I also heard gurgling near the washer area. Maybe I'm flushing too long or with too much pressure? I do not use a water pressure regulator when I do this.
Anyone else have this issue?
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Old 10-21-2021, 09:48 AM   #2
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Quote:
Originally Posted by 77Travco View Post
I noticed a smell in my interior the last few times that I have flushed my black tank. When standing outside the coach during the procedure... I also heard gurgling near the washer area. Maybe I'm flushing too long or with too much pressure? I do not use a water pressure regulator when I do this.
Anyone else have this issue?
Unless your coach is plumbed differently, the washer is plumbed into the grey tank, not the black, so there should be no "gurgling" from the pipes draining the washer. However, if it is plumbed to the black, that could account for the smell as noxious odors from the flushing are forced back through the p-trap in the stand pipe drain for the washer--that would be the gurgling sound. There would also be an air admittance valve in that line which could be bad and allow odors to escape.

If your washer is plumbed to the grey tank, which is more traditional, there would be no way flushing the black would affect the plumbing of the grey. Given that, what you are hearing may not be from the washer drain at all, but may be from the vacuum breaker/check valve for the black tank flush. If that is bad, odors can leak out of the diaphragm and enter the interior of the RV, causing the smell. It could also be the cause of the gurgling you hear. This vacuum breaker would be my first suspect.

As far as how you use the flushing system, it should only be used with the drain valve open though many close the drain to fill the tank a bit--a potentially dangerous practice if you ever get distracted. Water pressure is restricted by the water jet in the side of the tank, but excessive pressure can damage the vacuum breaker that was previously discussed.
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Old 10-21-2021, 11:13 AM   #3
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I can't explain the smell inside your coach any differently than the possibilities already mentioned. However, is there any possibility the "gurgling" sound you are hearing while outside is coming from the vents on your roof? I don't get it so much from emptying my black tank (probably because I never let it get THAT full), but when I empty my nearly full gray tank, I will definitely hear the loud gurgle coming from up above, which is understandable as it has to get air in to release that much water that quickly.

Good luck with finding the cause of your issue!
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Old 10-21-2021, 02:01 PM   #4
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If you have the grey tank valve open you could be forming a vacuum and sucking the water out of your traps.
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Old 10-21-2021, 03:04 PM   #5
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I flush the black tank with the grey tank valve closed and the black tank valve open. I will do some digging around to see if I can locate that vacuum breaker / check valve.
Anyone know where it might be located on a 2017 Bounder 33C ?
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Old 10-21-2021, 03:24 PM   #6
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Quote:
Originally Posted by 77Travco View Post
I flush the black tank with the grey tank valve closed and the black tank valve open. I will do some digging around to see if I can locate that vacuum breaker / check valve.
Anyone know where it might be located on a 2017 Bounder 33C ?

Until someone can post the location, you can try the following.


If you can get visual access behind the panel in the wet bay where the hose connection is for the tank flush, you may be able to follow the line from the flush inlet to where it enters the ceiling of the coach compartment. That would be the location of the vacuum breaker, inside the coach. Next to where that line enters the ceiling will be a line coming down back into the compartment and running to the flush nozzle at the tank.
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Old 10-21-2021, 05:07 PM   #7
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On my '16 Bounder 35K when I flush the black tank I do here a whooshing sound as the water flows through the flush lines. Completely normal IMO. If you look at the plumbing schematic you'll see this line goes up the wall a bit to be above the tank and then back down to the tank. This is near the rear of the W/D (in a 35K). This is so the black tank will not drain out through the flush hose kind of an anti-siphon valve.
I wonder if the smell inside the RV is a loose tank vent? On the 35K the vents are in the walls by the 1/2 bath. A little investigation may be in order to diagnose that one.
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Old 10-26-2021, 04:16 PM   #8
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Flush check valve location

On a 33C the flush check valve is behind the set of drawers in the bedroom. Remove the drawers and you'll find the check valve about 2 feet above the floor.

FYI - Under the drawers is an amazing array of cables!
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Old 10-26-2021, 08:23 PM   #9
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My experience

I had similar issue. I noticed my toilet bowl burped up when the tank level was high. The vent pipe was 2 off the bottom of the 7 high tank. I measured this with a tape measure from the roof. I was able to pull up on the pipe about 3 inches. This restored the vent function.
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Old 10-27-2021, 10:17 AM   #10
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Gurgling means one of two things:

Somehow you are pressuring up your drain system and your vent is not releasing this pressure,

or

While draining the bulk of your black or grey the levels are causing a low pressure above their levels. This too points to a faulty venting system, most likely plugged at the vacuum breaker or check valve.

Also check seals in toilet and ensure P traps have fluid in them.

I have never seen this but check the plumbing of the flush pipes.
Use low pressure to flush and you only need to do this briefly not for several minutes. I only give it a full-on flush at the end of the year when setting up to store for winter.

When done draining, put chemical in first flush to reduce odour.
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