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bird_dg · 10-20-2014, 05:28 PM

We regularly fill up our gray water tank after around 3 days or so; that's not bad of course except I happen to always be the one who gets to shower in ankle-deep water. Wife simply cannot grasp (or choses not to) the concept of a short shower. Now its a non-issue while camping with hook-ups but becomes a problem when camping without.
So, I got to thinkin'; if the gray tank is full and the black tank is say at the 1/4 level, couldn't I open the gray tank dump valve (with the hose cap secure) then the black tank valve and expect gravity to transfer gray water into the black tank until the levels in both tanks equalize or I close the valves?
The immediate downside I can see is I will have some residual water remaining in the plumbing and spill when I go to hook the hose up to dump. Anyone try something like this before? Any thoughts, good idea/bad idea/opinions? This is our first Airstream and the last thing I want to do is mess something up.
Thanks

terryV · 10-20-2014, 05:42 PM

Yes, you will have some nasty stuff in the pipes that will come screaming out when you take that cap off.

Also, you will probably get paper, and whatever else is in the blackwater tank, stuck in the slide valve, preventing the black water valve from fully closing. Now, the yucky water coming out of the uncapped pipe will not stop until the tank is empty.

Very messy, very embarrassing.

Jim Foster · 10-20-2014, 05:42 PM

One way to do this, and I explained it in another thread some time ago, is to use a separate fresh water pump connecting the intake to a pickup in your gray tank, making sure it is an inch or so above the bottom of the tank so as not to pick up any solid bits, and connecting the output to a "T" between the shut off valve to the head, and the head. When not connected to the sewer, shut off the regular water inlet to the head, and turn on the switch to the second pump. When you flush, it will automatically start the second pump and use water from the gray tank, thus saving fresh water and moving water from the gray tank to the black tank.

Someone out there sells such a setup for motorhomes, but one can be easily fashioned for an Airstream.

AnnArborBob · 10-20-2014, 05:45 PM

Bad idea on many levels. Not the least of which is that you will be introducing black water into the grey tank. Also, when you do remove your cap to dump, you will dump all over the ground a couple of gallons of black water which will be in the tube from your little maneuver.

NeverInn · 10-21-2014, 12:10 PM

Respectfully, I do not agree with AnnArborBob.

I use your theory all the time. However, if you use the cap to hold back the fluids you will not be a responsible camper because of the spillage you will get when take off the cap and before you can get the hose on.

Here is what I do. First I sawed off the (white) Thetford coupling off the drain pipe and replaced it with the industry standard Grentec or Anonda male coupler. I tried using a Universal Adapter but it leaks since it only has two hooks and flexes under the weight of the hose. I like using the Rhino Flex Sewer Hoses and with this modification I do not have to mess with the adapter.

Next I got a valve with a male Grentec or Anonda couper on one side and a Grentec or Anonda female coupler on the other side. The valve replaces the cap and shuts off the pipe so you can flow the grey water into the black tank. Because it has the male fitting you can then attach the hose to the valve at the dump station without spillage.

This is similar to what I use: (Mind doesn't have the clear tube and hose fittings for flushing. However, this should work fine.) Camco Dual RV Sewer Flush Pro - $28.99

When I see the sink drains start to slow or I get standing water in the shower I use the following procedure:

1) Remove the cap and connect the camco valve if it is not already on.
2) Make sure the camco valve is closed.
3) Open the gray water valve and wait for the the gurgling to stop indicating the the 3" pipes are full of grey water.
4) Open the black water valve and close once the sound of moving water stops.

After the fist time you do this you will have diminished returns because the level in the black water tank is closer to the level of the full grey water tank.

When I go to the dump station I attach the hose to the camco valve and dump as usual - black water first and then grey water last.

Washing dishes is another way a large amount of water is used. If you carry two plastic dish tubs and wash dishes like tenters do, you will conserve water and grey water tank space.

AnnArborBob · 10-21-2014, 02:06 PM

NeverInn, Thanks for the courtesy. However, using your approach seems to effectively turn your grey tank into a black tank as well, doesn't it? Am I missing something from your explanation? Using your approach how would you ensure that no black water gets into the grey tank when you "equalize" them?

Minipad · 10-21-2014, 03:47 PM

I use a a cap for my dump valve that has a threaded hose bib attached. (Available at most RV supply stores.) I take a short piece of hose and attach it to the hose bib and then dump just a few gallons at a time into a bucket. I carry the bucket in to the trailer and pour it down the toilet. Pretty easy an it helps to clean the dump mechanism in the toilet as well.

By the way, and speaking of black tanks ... I don't put any paper in our tank. Paper goes in a trash can next to the toilet to be thrown away. I also occasionally dump an entire bag of ice into my toilet just before I tow and the motion of the ice does a great job of cleaning the walls of the tank at the water level. Doing the same with just a few gallons of water in the black tank does a great job of scrubbing the bottom of the tank.

TinTin · 10-21-2014, 04:02 PM

You might want to consider using one of the portable waste holding tanks for your gray water.

Portable Waste Holding Tanks on Sale - PPL Motor Homes

Minno · 10-21-2014, 04:50 PM

We re-plumbed our bathroom sink to empty into our black tank. Adds some needed water to the tank, and conserves some space in the grey tank. I would opt for the Blue Boy portable tank over mixing your grey and black waters.

Kay

Minipad · 10-21-2014, 04:57 PM

I'm pretty sure the bathroom sink in most of the late-model trailers with split bathrooms does plumb to the black tank. I discovered that in ours because if the p-trap dries out (evaporation or sloshing), odors from the black tank enter the trailer up through the drain.

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AnnArborBob · 10-21-2014, 05:07 PM

Quote:

Originally Posted by Minipad

I'm pretty sure the bathroom sink in most of the late-model trailers with split bathrooms does plumb to the black tank. I discovered that in ours because if the p-trap dries out (evaporation or sloshing), odors from the black tank enter the trailer up through the drain.

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I wish ours did (2014 Eddie Bauer) but alas it does not.

SStar · 10-21-2014, 07:10 PM

Equalizing the tanks works fine, I have been doing it for years. For my AS I bought an adaptor from Thetford to Valterra then connected a Valterra valve on it. Then as NeverInn said just open the two valves and let the tanks equalize. The higher level will flow to the lower level. Close the valves when the tanks stop equalizing. If a very small amount of black water gets in the grey tanks it's no big deal. Our first old SOB just had one tank for both black and grey as I believe some of the older Airstreams has.

SStar · 10-21-2014, 07:17 PM

I found a photo of the adaptor. I always keep a spare.

Pitou49 · 10-21-2014, 08:17 PM

I replaced the shower head, use a square bucket inside the rond sink to wash the dishes and drop the water in the toilet. We made 5 days without hookup.
I always carry a 5 gal bucket and like Minipad, if needed, I carry the grey water in the toilet, I also carry a 6 gal gery cane to add fresh water in the tank.
An other thing, when I have 2 services I don't connect the city water because the pump noise is a good reminder, And poor lees water than city hook-up.

almcate · 10-22-2014, 04:49 PM

Not entirely related, but comment on using grey tank to manage black... first is to wash dishes in a tub in the sink and pour into the toilet. Over about four days, keeps both tanks close to even when reaching full. Secondly, after emptying black first (even with fresh water back flush holding for a couple minutes), there seems to be some amounts of solids/paper that just don't clear. Have been opening grey for 5-10 seconds to backflow into the open black tank, closing grey and letting black drain again a couple times. Seems to work (unless I'm missing something?) to loosen solid debris better than just the hose backwash and with flow INTO black, can't see any downside.

TinTin · 10-22-2014, 06:46 PM

Quote:

Originally Posted by almcate

Not entirely related, but comment on using grey tank to manage black... first is to wash dishes in a tub in the sink and pour into the toilet. Over about four days, keeps both tanks close to even when reaching full. Secondly, after emptying black first (even with fresh water back flush holding for a couple minutes), there seems to be some amounts of solids/paper that just don't clear. Have been opening grey for 5-10 seconds to backflow into the open black tank, closing grey and letting black drain again a couple times. Seems to work (unless I'm missing something?) to loosen solid debris better than just the hose backwash and with flow INTO black, can't see any downside.

No problem with your technique at all, since the outlet line is attached, and you close the gray to keep black water from potentially pushing back into the gray tank.

Trying to equalize the levels in the gray and black tanks with the outlet closed will lead to some residual wastewater in the outlet area, which will spill when it comes time to drain the tanks.

Pitou49 · 10-27-2014, 02:47 PM

Picture of the tub I use

dbj216 · 10-27-2014, 03:53 PM

My Thetford sani-con tank buddy macerator pump acts like a gate valve when not running. Their instructions state to pump the black tank first, shut off pump, open gray valve, let gray water flush into black tank, shut gray valve, and pump out black tank again. I find this is a good way to help rinse the black tank. We are always at risk of jamming something in a blade valve. Who else knows more about the ins and outs of black tanks than Thetford?

Gee, wouldn't be nice if access to these cheap valves was easier under an Airstream?

I replumbed my bath sink drain to the black tank just to help equalize usage in my old Trade Wind.

I think the new Bambi has just one tank for both black and gray water.

David

Protagonist · 10-27-2014, 04:54 PM

Left unstated in all of this, if your black tank is above floor level (some are) and your gray tank is below floor level (most are) then these gray-water transfer schemes won't work, because you can't make the gray water flow uphill into the black tank.