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Author Topic: Grey water fluch question.  (Read 525 times)


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Grey water fluch question.
« on: January 24, 2018, 10:40:22 AM »
I'm just curious - When I drain the grey tank there is the initial flush and then after a minute or two it slows down.
Then there is a second whoosh sound and it appears more water is running out like it did at the first pull of the handle.

I keep the grey and black tanks closed for about a week at a time, then after I dump the black tank I follow with
the grey tank and what happens is described above.  I don't believe that the tanks are full as I'm alone, and have never
seen any signs of a backup - which I would assume if it did backup the shower would be the lowest point and it would
show there, but never has.

Does this happen to anyone else?
2002 Rexhall Rose Air  Cummins 8.3  350hp
West MI Summer   Central FL Winter

Rene T

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Re: Grey water fluch question.
« Reply #1 on: January 24, 2018, 10:48:16 AM »
As far as the flow of water, I'm thinking that the initial flow is the water just running out with no restraints. When it slows down it may be because the vent pipe is not letting enough air into the tank so the water slows down. The drain pipe is 3" and the vent may be no bigger than 1-1/2" possibly even 1-1/4". Then when the water level gets low enough, air will get into the tank through the top 1/3 of the drain pipe and allow it to drain fast again. That's all I can think of which may be causing this.
Rene, Lucille & co-pilot Buddy
AKA  Pep N Mem
2011 Chevy Duramax 2500 HD 4X4
2011 Montana High Country 343RL
From the Granite State of NH
& Florida Snowbird in Lakeland FL


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Re: Grey water fluch question.
« Reply #2 on: January 24, 2018, 11:28:16 AM »
Does this happen to anyone else?

I get the same exact thing, and I think Rene’s theory is dead on
Fulltiming in a 2005 Newmar Dutch Star 3810, Cat 350
Eezrv TPMS, 970W Solar, Tri-Metric Battery monitor
2002 Dodge RAM 1500 Quad Cab toad
Stowmaster towbar & Brakemaster toad braking system

Gary RV_Wizard

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Re: Grey water fluch question.
« Reply #3 on: January 24, 2018, 11:40:22 AM »
All of my RVs have done the same, and I believe Rene's explanation is on target.
Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

john owens

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Re: Grey water fluch question.
« Reply #4 on: January 24, 2018, 01:03:24 PM »
From your post it sounds like you do not have a see thru fitting on your drain system. They come in real handy when cleaning out both tanks. It does sound like there is a slight pause due to a vacuum affect on your plumbing. As a simple example our drinking water comes in 2 gallon plastic containers. When you first open the valve to fill the cup you get a decent amount of flow, but in a short while it slows to a trickle. Punching a small hole in the top of the container solves the problem... :))
2011 Winnebago 37F Class A  2012 Unlimited JK 2001 HD roadking  1964 Manx 1641cc buggy 1985 22'Lazy Daze Class C 2007 Chaparrel 26' deck boat..Thats all folks!!


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Re: Grey water fluch question.
« Reply #5 on: January 24, 2018, 05:22:20 PM »
Yep, I get the same pause. I do have a clear fitting and I can see it happening. Rene has nailed it.
Apex, NC
2010 Winnebago journey Express 34Y
2018 Ford Edge SEL