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Old 01-14-2012, 01:07 PM   #1
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Combining black and gray tanks?

My 31' Classic has a 54 gal freshwater tank, and a 39 gal gray tank, and 37 gal black tank (or vice versa). The problem is that when we are travelling, we usually use much less water in the black tank ( no No. 2 in our black tank!) and therefore overflow the gray water tank.

Has anyone figured out a way of letting the gray water tank share the black water tank? When I've been desperate, I've opened both drain valves with the outflow pipe sealed with the cover, but that is a bit messy when it comes time to dump the tanks.

Thanks
Paul
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Old 01-14-2012, 02:01 PM   #2
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My 31' Classic has a 54 gal freshwater tank, and a 39 gal gray tank, and 37 gal black tank (or vice versa). The problem is that when we are travelling, we usually use much less water in the black tank ( no No. 2 in our black tank!) and therefore overflow the gray water tank.

Has anyone figured out a way of letting the gray water tank share the black water tank? When I've been desperate, I've opened both drain valves with the outflow pipe sealed with the cover, but that is a bit messy when it comes time to dump the tanks.

Thanks
Paul
Paul.

It's very easy to figure out.

DON'T GO THERE.

You will create an absolute "HEALTH HAZARD", in doing what you would like to do.

Andy
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Old 01-14-2012, 02:16 PM   #3
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Paul,
I had a set up years ago where I could pump excess gray water into the black tank. AFAIK it came from the factory that way. I don't think it would be too hard to set up a marine type submersible pump with a check valve. The only way I would do it would be a one way transfer from the gray tank to the black tank, which if I read you right is what you are wanting to do.

I agree, our gray tank, which is a miniscule 10 gallons, the black is a bit better off at 20 gallons, so moving graywater is a necessity.

When parked in a non hookup campground we use one of the rolling blue tanks. If we are parked where it is allowed, and it is becoming harder and harder to find places that allow it, we dump gray on the ground.

As long as you use a check valve, I don't see any health hazard in adding gray water to the black tank, in fact it might actually help in that it dilutes the contents.

Aaron
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Old 01-14-2012, 02:24 PM   #4
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We sometimes pour dishwater into the black tank through the toilet as a way to extend the capacity of the gray tank. Not a very elegant solution, but simple and foolproof. We can delay having to empty the gray tank by a couple of days this way.
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Old 01-14-2012, 03:26 PM   #5
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Originally Posted by Inland RV Center, In

Paul.

It's very easy to figure out.

DON'T GO THERE.

You will create an absolute "HEALTH HAZARD", in doing what you would like to do.

Andy
No offense Andy, but what in the world are you talking about? Airstream has many models with combined grey/black tanks. No gumming up and flush it all down the sewer. If I'm I not enlightened ... please enlighten me. Wondering if my health is at risk in my 2004 International.
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Old 01-16-2012, 03:48 PM   #6
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No offense Andy, but what in the world are you talking about? Airstream has many models with combined grey/black tanks. No gumming up and flush it all down the sewer. If I'm I not enlightened ... please enlighten me. Wondering if my health is at risk in my 2004 International.
Airstream used a single tank on an old 28 foot trailer.

Then, of recent vintage, they use it on the very smallest trailers.

However, they warn, DO NOT OVERFILL.

If those single tanks are overfilled, the liquid and some solid parts will back up into the "P" traps of the shower or tub.

In either case, to most owners, that is a serious health risk.

And, needless to say, a nasty job to clean up and disinfect.

Andy
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Old 01-17-2012, 06:17 AM   #7
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Interesting to know ... and I could see this being an issue based on elevation and location of pipes. However, in 8 years of heavy use, we haven't had a problem in our 2004 28' (is that old?). Then again, I can't recall a time we allowed ours to fill full enough to make what you are hypothecating possible. Our two sink P traps are two feet higher than the shower and toilet. Backflow would come to the toilet bottom and shower tub before it could come to sink traps. Frankly, I recommend the large single tank set-up ... it is a benefit and allows me to keep my tank cleaner. BTW, my shatt doesn't stink. LOL
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Old 01-17-2012, 11:27 AM   #8
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Interesting to know ... and I could see this being an issue based on elevation and location of pipes. However, in 8 years of heavy use, we haven't had a problem in our 2004 28' (is that old?). Then again, I can't recall a time we allowed ours to fill full enough to make what you are hypothecating possible. Our two sink P traps are two feet higher than the shower and toilet. Backflow would come to the toilet bottom and shower tub before it could come to sink traps. Frankly, I recommend the large single tank set-up ... it is a benefit and allows me to keep my tank cleaner. BTW, my shatt doesn't stink. LOL
I have talked to people with more college degrees than I have on the subject, and they tell me grey water has more different kinds of bacteria than what's in the black tank. Among the grey tank contents are raw food, cooked food, other less pleasant things, as well as the stuff that is on us when we wash our hands and bodies. Black tank contents are really more limited, since most of that has had the side benefit of having been through our digestive system. If you think about it, if your home shower drain backs up, you have the same problem. If you think about it that way, what is in the bottom of the shower, while definitely bad, isn't as life-threatening as some would have you believe, for whatever reasons they have.
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Old 01-17-2012, 12:30 PM   #9
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Quote:
Originally Posted by trvler View Post
My 31' Classic has a 54 gal freshwater tank, and a 39 gal gray tank, and 37 gal black tank (or vice versa). The problem is that when we are travelling, we usually use much less water in the black tank ( no No. 2 in our black tank!) and therefore overflow the gray water tank.

Has anyone figured out a way of letting the gray water tank share the black water tank? When I've been desperate, I've opened both drain valves with the outflow pipe sealed with the cover, but that is a bit messy when it comes time to dump the tanks.

Thanks
Paul
Back to the original question - here's a product you should have in your backup equipment box regardless:
Amazon.com: Valterra T58 Twist-On Waste Valve: Automotive

Now put on your latex gloves. It makes you feel official. If you have separate black and grey tanks and want to transfer gray water to black, first make sure there the grey water level is well above the black - usually the case after several days of camping.

Next remove your dump cap and twist this valve on the outlet. Make sure the handle has clearance and that the valve is closed.

Then open the grey valve, and grey water will fill the connecting pipes between the black and grey tanks.

Then open the black valve, and grey water will flow into the black tank.

Close the black valve while the sound of moving grey water is still present - avoiding black backflow.

Then close the grey valve. You now have more grey tank capacity.

When dumping, attach the sewer hose to the twist-on valve, then open the twist-on valve to dump the connecting pipes.

Then dump black, and rinse the black tank if you have a fitting. Then close the black valve.

Then dump grey and close the grey valve.

Take the twist-on valve off and put the cap back on the outlet.

Rinse the twist-on the valve, store in a plastic zip bag.

Don't forget to rinse down the dump area.

Remove your gloves - or keep them on if you like the look.

On your way!
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Old 01-17-2012, 12:34 PM   #10
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i have entertained the idea of doing this in my '66 caravel. i've been told that the grey tank in my trailer was not an original piece of equipment....but my thinking was if i could figure out a way to make one tank for both grey and black water and just make sure it's bigger than the fresh water tank...then when you run out of fresh water then you know it's time to empty...seems to make sense to me...the only question i have is how much bigger should the waste tank be in order to be big enough
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Old 01-17-2012, 12:42 PM   #11
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Using 1 tank for both black and gray, as some trailer models do is probably the dumbest money saving idea a manufacturer ever came up with.
Black water pretty well has to go to a dump station.
Gray can be handled many ways and is even known to disappear during the hours of darkness.

I can understand why transfering could be handy at times, but would never own a one tank trailer.
Gray water only becomes gross when it is confined in a hot tank for a few days. If discharged immediately it is not a problem.
In many areas it is ok to discharge sink water with out going through a septic tank. Our kitchen sink and washing machine have gone "over the hill" for years and it is difficult to even find the discharge spot.
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Old 01-17-2012, 12:46 PM   #12
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i have entertained the idea of doing this in my '66 caravel. i've been told that the grey tank in my trailer was not an original piece of equipment....but my thinking was if i could figure out a way to make one tank for both grey and black water and just make sure it's bigger than the fresh water tank...then when you run out of fresh water then you know it's time to empty...seems to make sense to me...the only question i have is how much bigger should the waste tank be in order to be big enough
The tank size, depends on how many times you visit the toilet each day.

The next consideration, is where the tanks are with respect to the axle.

Your Caravel did not have a gray tank when built. Gray tanks were not common with Airstream until the 1974 models.

Andy
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Old 01-17-2012, 12:57 PM   #13
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Using 1 tank for both black and gray, as some trailer models do is probably the dumbest money saving idea a manufacturer ever came up with.
Black water pretty well has to go to a dump station.
Gray can be handled many ways and is even known to disappear during the hours of darkness.

I can understand why transfering could be handy at times, but would never own a one tank trailer.
Gray water only becomes gross when it is confined in a hot tank for a few days. If discharged immediately it is not a problem.
In many areas it is ok to discharge sink water with out going through a septic tank. Our kitchen sink and washing machine have gone "over the hill" for years and it is difficult to even find the discharge spot.
Rick.

Apparently, the RVIA has no set standards for the double use tank.

I am sure, that any Doctor or medical professional that owns an RV, would agree to the health hazard of the double use.

The answer I learned just yesterday, is that in the absence of "NO" standard for the double use, then no harm is "apparently" done, should that method "backfire".

Given time, which the RV industry usually needs, such a method wil eventuallyl be "OUTLAWED". At least that's my humble opinion.

Safety is still safety, even with bacteria.

Andy
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Old 01-17-2012, 02:10 PM   #14
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......>snip<.........
Gray water only becomes gross when it is confined in a hot tank for a few days. If discharged immediately it is not a problem.....>snip<.......
This is so true... we use a dish pan when we do dishes and use the sink for rinsing... If we are dry camping we typically use the wash water to water a bush rather than sending it to the grey water tank because at that point it is not offensive and not bacteria-laden. (It may have minor food particles, etc, but nothing extreme.) This saves a lot of space in the grey tank. Once waste water is in the grey tank, bacteria begins to take over and do its thing ... and it becomes very rank rather quickly ... especially in warm weather. The odor of grey water that's been brewing 2 or 3 days is not a pleasant thing...almost as bad as black tank odors.
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