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Old 08-23-2017, 03:15 PM   #1
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Tank confusion

I thought that the black water tank was only fed by the toilet. Now I'm confused.

I keep the fresh water tank in our FC filled as an emergency supply and flush and change it periodically. Sometimes I use the pump and open faucets in the galley and head in addition to the drain valve to speed the flushing process. (I know there are petcocks under the trailer that can be used for this purpose as well.)

Today I was emptying the fresh water tank and watching the tank levels on the monitor. At some point I opened the gray water valve, dumped the contents and then thought to leave the valve open to allow water to continue to flow out. By this point only the faucet in the head was turned on.

To my surprise there was almost no flow out of the grey tank. I let things go for a while and still no flow and nothing registered on the monitor for the grey tank. I happened to check the black tank level, however, and it registered 100%. What? Must be a mistake. So I turn off the pump and go and pull the black tank valve. Whoosh! Fortunately, the blank tank had been thoroughly flushed after our last trip or it could have been bad.

So, I thought that the sinks and shower fed the grey tank and only the toilet fed the black tank. Empirical evidence would indicate that's wrong as no one has used the toilet since our last trip. I can only conclude that the sink in the head must also feed into the black tank and it has been accumulating water over my last several water exchanges. If true, that plumbing arrangement seems dumb to me but I don't know what else to think. Your thoughts?
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Old 08-23-2017, 03:35 PM   #2
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The schematic in the owners manual for our 25' RB clearly shows the lavatory sink drains into the black tank. Have you looked in your manual?
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Old 08-23-2017, 03:46 PM   #3
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My understanding is that sending the bathroom sink water to the black tank helps keep things more liquid than solid in the black tank.
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Old 08-23-2017, 03:53 PM   #4
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Quote:
Originally Posted by Adventure.AS View Post
The schematic in the owners manual for our 25' RB clearly shows the lavatory sink drains into the black tank. Have you looked in your manual?
Yes. I've read through it on multiple occasions, but I apparently missed that particular item. My bad. Thank you for your reply and reading recommendation.

Quote:
Originally Posted by DaveMc View Post
My understanding is that sending the bathroom sink water to the black tank helps keep things more liquid than solid in the black tank.
That does make sense. Thanks.
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Old 08-23-2017, 05:46 PM   #5
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We Airstreamers have had quite an ongoing debate about mixing black and gray water. The risk is if your trap in the bath sink drys up for some reason. Now you will get sewer gas into the trailer. Yuk.

When I rebuilt the bath in the Trade Wind, I purposely drained the bath sink into the black tank I wanted to share waste water capacity, and it was handy plumbing wise to do so.

After three years, no problems noted, except just this spring while flushing the antifreeze out of the trailer, I did the same thing you did. I left the bath sink run while flushing. Then I opened the gray dump valve and there was no water there. The black tank was full. I guess I forgot what I was doing.

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Old 08-23-2017, 06:00 PM   #6
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Good information here . . .

Tanks a lot!

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Old 08-23-2017, 06:03 PM   #7
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Quote:
Originally Posted by mikeinca View Post
I thought that the black water tank was only fed by the toilet. Now I'm confused.

I keep the fresh water tank in our FC filled as an emergency supply and flush and change it periodically. Sometimes I use the pump and open faucets in the galley and head in addition to the drain valve to speed the flushing process. (I know there are petcocks under the trailer that can be used for this purpose as well.)

Today I was emptying the fresh water tank and watching the tank levels on the monitor. At some point I opened the gray water valve, dumped the contents and then thought to leave the valve open to allow water to continue to flow out. By this point only the faucet in the head was turned on.

To my surprise there was almost no flow out of the grey tank. I let things go for a while and still no flow and nothing registered on the monitor for the grey tank. I happened to check the black tank level, however, and it registered 100%. What? Must be a mistake. So I turn off the pump and go and pull the black tank valve. Whoosh! Fortunately, the blank tank had been thoroughly flushed after our last trip or it could have been bad.

So, I thought that the sinks and shower fed the grey tank and only the toilet fed the black tank. Empirical evidence would indicate that's wrong as no one has used the toilet since our last trip. I can only conclude that the sink in the head must also feed into the black tank and it has been accumulating water over my last several water exchanges. If true, that plumbing arrangement seems dumb to me but I don't know what else to think. Your thoughts?
Hi Mike,
Thanks for your post and observation. I was curious about the exact same thing you are talking about here. Because there seems to be some contradiction in what the owner manual states, what the schematic shows and what is actually occurring (as in your case).

I just recently purchased a 2018 Flying Cloud 25, so in anticipation of taking delivery of our new trailer, I downloaded the owners manual and began reading.

This diagram is on one of the pages of the owner's manual which gives a pretty clear depiction of how the waste water system is designed:

Click image for larger version

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It clearly shows that the lav empties into the black water tank.

Further reading in section 5 of the owner's manual states:

Drain and Waste System
Your trailer has a drain and waste system that includes waste-holding tanks made from corrosion-free molded plastic, with trouble-free dump valves�
The main (Black Water) holding tank enables you to use the toilet for several days away from disposal facilities� The wastewater from the sink, shower, bath and lavatory drains into the auxiliary (Gray Water) holding tank�


I don't believe that section 5 is correct in stating that the lav drains to the gray water tank. From your observation, it would seem that the lav does indeed drain into the black tank.

I'm not sure what the 2017 owner's manual depicts, but I would assume it is the same, since not much has changed from 2017 model to 2018 (except for the multi-stage converter).
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Old 08-23-2017, 06:08 PM   #8
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Now that's Funny

Quote:
Originally Posted by OTRA15 View Post
Good information here . . .

Tanks a lot!

I guess I was a little late to the discussion.
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Old 08-23-2017, 06:22 PM   #9
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. . . just a little black humor I guess . . .

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Old 08-23-2017, 06:33 PM   #10
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Quote:
Originally Posted by dbj216 View Post
We Airstreamers have had quite an ongoing debate about mixing black and gray water. The risk is if your trap in the bath sink drys up for some reason. Now you will get sewer gas into the trailer. Yuk.

David
You get sewer gas in the grey tank, too. And if you're using the trailer at all, you probably wash your hands in the bathroom sink after using the toilet, that would be more than ample water for the trap.
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Old 08-23-2017, 07:04 PM   #11
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Quote:
Originally Posted by sncnidaho View Post
Drain and Waste System
Your trailer has a drain and waste system that includes waste-holding tanks made from corrosion-free molded plastic, with trouble-free dump valves�
The main (Black Water) holding tank enables you to use the toilet for several days away from disposal facilities� The wastewater from the sink, shower, bath and lavatory drains into the auxiliary (Gray Water) holding tank�

Yes! Thanks so much for posting that, sncnidaho! It proves that I haven't gone completely senile...yet.

I could have sworn that I had read that information about the lavatory sink and going back to the manual again just now mine has the exact same wording. So there IS a discrepancy between the schematic and the text and I just hadn't picked up on it before.

Clearly, based on my experience, the schematic is right and the text is wrong, and fortunately the lesson was learned before anything really bad happened!
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