Connecting black and grey tank

[Gallego]

Hi
We are a family of 4 (2 kids) so with showers and regular use our grey tank lasts maximum 2 days, in contrary, our black tank never goes over 20. It would be great to be able to "dump" some of our grey water into the black tank when needed. Is this crazy or makes sense?

[Msherw]

I know your frustration as our last boon docking campout resulted in the same issue. I think the grey and black tanks are physically separate (except in the 16 where only one tank exists). Other than using a hand or electrical pump to transfer from grey to black, I see no other way to do this. Also, the black water tank is smaller (at least on some AS models) so a transfer of grey may not help you as much as you anticipate.

Navy showers of 1-2 mins or wash ups at the sink are always recommended. I would rather run out of grey capacity before I lose black water.

[dbj216]

It makes sense to me. Some newer Airstreams drain the bath sink water into the black tank just to share capacity a bit. The showers are the biggest consumer of water, so brief showers when necessary is the way to go. I know long, hot showers are a luxury. But we are "roughing" it when we are Airstreaming.

I am installing more waste water capacity in my old Overlander. The bath sink will drain into the black tank. I need the extra water to keep the black tank wet and not let solid wastes harden. The shower and galley sink will drain into the gray tank. Between the two new tanks, I will have 55 gallons of waste water capacity.

Many good Airstreamers say never to mix wash water with toilet water. Sewer odor is one reason should my bath sink trap dry out and open up.

David

[Camano20]

For what it is worth, we have a Safari 20 and use a wash pan in the sink when we do dishes then dump into there toilet. Saves a bit on the grey tank usage. A couple of campgrounds have also had grey water dumps for tenters that we dump the dish water into.

[Acheron2010]

Do a web search of "astreaminlife." Those folks combined their black and gray tanks on their classic when they converted their head to compost.

[Venturewest]

I was reading my original 1968 Airstream Owners Manual last night and Airstream had an interesting procedure for this very issue. They recommended opening the black water waste valve but leaving the waste cap on. This allows the gray water to fill the black tank. They recommended a bucket under the cap when its time to dump the tanks. This would catch the small amount of water between the valve and the cap. (Gross)

I have seen a modern take on this in RV forums though. You add the valterra fitting that has the waste valve on it. Then you open both your gray and black tank valves. This will allow the gray to flow up into the back and you combine capacity. You then rely on the the outer valterra valve when you dump. I have a trailer with remote valves that have broken and I now use the valterra valve fitting, and it works great. I hope that makes sense.

[islandtrader]

Originally Posted by Venturewest

I was reading my original 1968 Airstream Owners Manual last night and Airstream had an interesting procedure for this very issue. They recommended opening the black water waste valve but leaving the waste cap on. This allows the gray water to fill the black tank. They recommended a bucket under the cap when its time to dump the tanks. This would catch the small amount of water between the valve and the cap. (Gross)

I have seen a modern take on this in RV forums though. You add the valterra fitting that has the waste valve on it. Then you open both your gray and black tank valves. This will allow the gray to flow up into the back and you combine capacity. You then rely on the the outer valterra valve when you dump. I have a trailer with remote valves that have broken and I now use the valterra valve fitting, and it works great. I hope that makes sense.

Most likely something like this....

[dbj216]

I use a "tank buddy" macerator pump to drain the black and gray water tanks. I do this as I have sometimes found the campground sewer connection is higher than my rather low Airstream. The pump eliminates this as a problem.

With the pump attached to my waste water bayonet connection, I can dump and pump the black tank until it is empty. Then I can leave the black tank valve open, open the gray tank, and the gray water floods into the black tank acting as a rinse. The pump acts as a valve preventing the water from draining out. Then the pump is turned back on and I empty both tanks. I always get a better rinse of the black tank doing this.

So yes, with a third Valterra valve that attaches to the bayonet waste water connection, you can combine the two tanks. And you can then connect the slinky hose and open the third valve and drain as usual.

David

[Venturewest]

Originally Posted by islandtrader

Most likely something like this....

Attachment 304915

You actually only need this part on the waste outlet. You just replace your cap with this fitting. Then you just open your gray and black tank valves. If you have remote valves this is great too because it prevents an ugly mess if one of the main valves fails.

[Adventure.AS]

Originally Posted by dbj216

...
With the pump attached to my waste water bayonet connection, I can dump and pump the black tank until it is empty. Then I can leave the black tank valve open, open the gray tank, and the gray water floods into the black tank acting as a rinse. ...

The gray 'rinse' water is now full of fecal matter from the black tank and will flow the other way too, contaminating your gray tank with e-coli, etc. which defeats the purpose of having the two separate tanks.

[Rocinante]

Yup, I wouldn’t combine the two tanks this way unless I had a composting toilet (no black water anymore) and had thoroughly cleaned out the black tank before never using it for black water again. [emoji6]

[azflycaster]

Many vintage trailers have the black tank on top of the floor. If connected together the grey would fill first and then the blalck which would fill at the same rate as the floor of the shower.

[Mollysdad]

I'd suggest the Barker Tote tank external tank. It will allow you to drain 20 gallons of grey before needing to dump.
Let the kids take it to empty and their showers will be shorter.

[Rocinante]

Now that’s an idea I can support!

[LAWBC]

My wife started using a dish pan in the round sink just because it was too large and waste of water to fill it. As a result for the past couple of years we have used it to transfer the dish water to the toilet and found that alone gave us a couple of more days of capacity dry camping. We practice this the odd time even when hooked up. Bonus, putting more water into the black tank seems to have kept the sensor in the black tank working , or at least I have had no issues with it.

[Msherw]

Originally Posted by Adventure.AS

The gray 'rinse' water is now full of fecal matter from the black tank and will flow the other way too, contaminating your gray tank with e-coli, etc. which defeats the purpose of having the two separate tanks.

Totally agree. Dual tanks keeps the black out of the shower and lav grey tank and odors at bay. I like the idea of dumping a kitchen sink holding pan into the toilet if you think your gray will be overtaxed. The kitchen sink water is second only to the shower as a high use of grey water tanks.

On a parallel note: how many of you wash your black tank out using the little hose connection just below the city input?

I didn’t use this washout until I got an AS and found the connector to be convenient to use while either dumping black at the end of a campout or just before I close all the valves to journey to my next site. Do you use a different hose to do this rather than your fresh hose? (Just in case of back flow)

I think it is a great way to help insure the black tank stays odorfree without a bunch of chemicals. However, I have head of some folks connecting to that washout connector thinking they were hooking to the city fresh. If the dump valves were closed when this happens, water backs up and eventually squirts out the vent on top of the AS. Bad news. Rule is know your TT connectors and think about the process.

[Rocinante]

There is normally a vacuum break check valve in the rinse line for the black tank, just inside the trailer. It’s rated at 25 psi. (Don’t ask how I learned that number, but it’s not a lesson you want to learn the way I did.) So, under normal conditions it is technically safe to use the same hose for fresh and tank rinse. That said, I just cannot make myself do that, so I use a separate water hose, marked “dirty,” for that chore.

[Boxite]

Originally Posted by Msherw

... However, I have head of some folks connecting to that washout connector thinking they were hooking to the city fresh. If the dump valves were closed when this happens, water backs up and eventually squirts out the vent on top of the AS. Bad news. Rule is know your TT connectors and think about the process.

I've heard this too...but it's difficult to believe if systems work as intended..... because if you look at the plumbing diagram it shows that the grey-vent ties to the black-vent above the black tank...
This means that if you have the valves closed and use the back-flush and fill the black tank...it will overflow into the grey tank well-before it fills the line to the roof-vent...
The black tank will then fill your grey tank....which will fill your shower-pan and flood your trailer before/if it spurts out the roof.

Also, the backflow-preventer on the backflush line is usually plastic and will malfunction and/or fail and leak water into your walls and sub-floor.... or (as happened to me) simply plug and fail to allow the black tank to be flushed. Again, if you study the plumbing schematic, you'll see the inlet to the backflush is 18-20" above the black tank...so there's simply no way the black tank can ever contaminate the water-supply-hose which is providing pressurized water to the system. (The backflow preventer is a "code" requirement...but in actuality is useless and commonly the source of a problem.) If it fails, simply replacing it with an "elbow" or "shark-bite-fitting" will return the system to service without re-introducing a failure\-mode. There simply is no health issue to a fitting which is 18-20" above the black tank and also distanced from that tank by a double-set of 90-degree elbows at an elevation above the tank and, on top of that, is pressurized and never exposed directly to black water.

If you ARE concerned about germs... you should do something almost never mentioned.... use a bleach-solution applied to your city-water-inlet. (I realize some folks put bleach in their fresh tanks...but they do that at that tank filler...not thinking about the city-water inlet). The same can also be done to your backflush inlet.

[Al and Missy]

Originally Posted by Adventure.AS

The gray 'rinse' water is now full of fecal matter from the black tank and will flow the other way too, contaminating your gray tank with e-coli, etc. which defeats the purpose of having the two separate tanks.

On my 30 I drain the black tank and then open the gray valve for 5 seconds and close it. The pressure of the gray water fills the transparent ell on my dump output and pushes gray water into the black tank. When I close the gray valve there is an initial flow of gray water and then some more effluent from the black tank. I do this several times until the gray partial dump no longer fills the transparent ell fitting. At this point the black tank is pretty clean. As long as the gray tank is full, the flow is always into the black tank until I close the gray valve. My 25 had the third valve. I would do the same as with the 30 except I had the third valve closed during the gray rinses. In four years of doing this, over 160 nights camping, I have never had a problem with gray tank odors.

Al

[BigAl]

There is one instance when the back flow preventer will do it's intended job. If the black tank water level is higher than the nozzle on the tank rinser and the supply hose is connected to it but not hooked up the city supply then water cannot siphon out of the tank. The reason for the code requirement is in the off chance that while you are rinsing the tank out the supply water is shut off at the main. Then waste water could siphon back into the supply system. When turned back on the main supply would be contaminated.
Same as why a bidet must have a back flow preventer.
Al