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Old 09-10-2013, 05:24 PM   #1
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2013 25' FB Flying Cloud
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Gray Tank Problems on New Airstream

Any ideas why every time we drain the big round sink, nasty water comes up in the shower; besides the fact that something's not right? The gray tank is empty; monitor system says so, and I've drained the system. It's a new unit (2013 Flying Cloud 25FB), so it will be repaired under warranty, but we're on the road on right now and I'm wondering if it could be something simple? What would cause this? Thanks.
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Old 09-10-2013, 05:48 PM   #2
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I'll bet your grey tank vent is plugged. As a result, when a few gallons of water go sloshing down into your grey tank, the air in the tank has no place to go, so it finds a path through the plumbing and out your shower pan. The icky water is whatever is left in the trap and perhaps some that has settled in the pipes. One way to test the theory is connect to open your grey dump valve and then empty that sink-full of water. If it doesn't cause anything funky in the shower, then its a vent problem. You might be able to pick up a fish tape at a hardware store and run it down through whatever is causing the blockage.

good luck!
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Old 09-10-2013, 06:46 PM   #3
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Thanks!

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Originally Posted by Belegedhel View Post
I'll bet your grey tank vent is plugged. As a result, when a few gallons of water go sloshing down into your grey tank, the air in the tank has no place to go, so it finds a path through the plumbing and out your shower pan. The icky water is whatever is left in the trap and perhaps some that has settled in the pipes. One way to test the theory is connect to open your grey dump valve and then empty that sink-full of water. If it doesn't cause anything funky in the shower, then its a vent problem. You might be able to pick up a fish tape at a hardware store and run it down through whatever is causing the blockage.

good luck!
That's exactly what happens. When connected to an RV Park sewer system and the gray tank valve is open, we don't notice the problem. Only when the valve is closed. Thank you.
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Old 09-10-2013, 07:00 PM   #4
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Hi, this same problem has been observed on 27FB as well, it appears the grey tank vent design is similar.

Basically, water draining from the galley sink fills up the drain pipe, and prevents the black tank from being able to vent. A better design would have the vent piped directly to the tank.

See http://www.airforums.com/forums/f446...ion-86758.html for additional links and details.
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Old 09-11-2013, 08:37 AM   #5
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I checked out the plumbing diagram on the link above--looks like a marginal design, as the pathway for water from the sink is down the same pipe that vents. Looks like the solution is either a plug in the shower pan, or a slow drain of the sink, or a combination of the two. I suppose the vent pipe could be clogged also, which might exaggerate the problem, but the symptoms described here sound exactly like those reported in the other posts.
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Old 09-11-2013, 11:55 AM   #6
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Unacceptable

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Originally Posted by Belegedhel View Post
I checked out the plumbing diagram on the link above--looks like a marginal design, as the pathway for water from the sink is down the same pipe that vents. Looks like the solution is either a plug in the shower pan, or a slow drain of the sink, or a combination of the two. I suppose the vent pipe could be clogged also, which might exaggerate the problem, but the symptoms described here sound exactly like those reported in the other posts.
If it's truly a design problem; that's ridiculous for a $70K+ trailer. However, after reading through the entire thread posted above, it sounds as the OP problem was a blocked vent. I still have to explore that possibility.
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Old 09-11-2013, 03:06 PM   #7
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The drain design is marginal as there is a 1-1/2" section of vertical pipe 13" long that serves as a wet vent for both the lav and galley sinks. Even if the vent is working properly that would be enough to lead to insufficient venting.

Of course if the vent is blocked that will make it worse.

I am not intimately familiar with the construction of the 25FB flying cloud however it appears to me that it might be possible to remove the air admittance valve from the shower drain and run vent pipe from there to a newly added T just above the existing T on the vent stack. That would clear up the problem.
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Old 09-12-2013, 03:43 PM   #8
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I am not intimately familiar with the construction of the 25FB flying cloud however it appears to me that it might be possible to remove the air admittance valve from the shower drain and run vent pipe from there to a newly added T just above the existing T on the vent stack. That would clear up the problem.
Unfortunately, the shower drain admittance valve is on streetside, and the vent pipe is on curb side :-(
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Old 09-12-2013, 03:52 PM   #9
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Hmm, would make for an aesthetically unacceptable mod then.
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