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Old 04-11-2019, 05:10 PM   #1
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Blowback in the WC

Hello fellow RVers.
We have a 2018 Coachmen Pursuit 32 WC.
It has three waste tanks - two for grey water (one for bathroom shower/sink, one for kitchen sink), and one for black.
Every time we flush the toilet, we get "blow-back" from the tank (an air bubble comes from the tank before the toilet drains). Both of the grey tanks appear to have vents to the roof, but the black tank doesn't - unless one of them is teed into the black tank, which I think is unlikely. When I drain the black tank, it sucks in air through the waste pipe before dumping. If we "flush" the toilet during dumping, the tank drains fine.

Am I right in thinking that the black tank might be missing a vent? Is it actually possible that the manufacturer missed this?

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Old 04-11-2019, 05:13 PM   #2
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It is possible the vent pipe is submerged in the tank being too long. Maybe a inspection camera down the toilet and have a look see.

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Old 04-11-2019, 05:20 PM   #3
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Another way to check is to use a shop vac and blow air back through the waste valve and see if air comes out roof vent or only through toilet bowl. Obviously make sure black tank is well drain before.
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Old 04-12-2019, 06:40 AM   #4
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B and B is right on. Vent pipe is extended too deep in tank. If you flush after tank is completely empty, betting no blowback, however as tank fills and end of vent pipe gets submerged, problem gets worse.
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Old 04-12-2019, 03:02 PM   #5
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It is my understanding that it is common for black and grey tanks to share a vent, to minimize roof penetration. It sounds like it is plugged, perhaps as described above.
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Old 04-14-2019, 07:44 PM   #6
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Probably what B and B said, the black tank vent is submerged in the tank, happened on my Georgetown, just another example of sloppy assembly by a manufacturer with no effective quality control.

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