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Old 08-09-2015, 04:23 PM   #1
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Bleeding greywater into black tank

Has anyone ever come up with a mod to feed greywater into the black tank - we tend to fill grey faster than black and end up dumping due to full grey but with not so full black. It would be helpful to make use of that capacity.
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Old 08-09-2015, 05:11 PM   #2
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I bought a twist-on blade valve for $20. It goes on the sewer outlet, and with the twist-on valve closed, you can open the black and grey valves, then the two tanks will mix in the main outlet. I've only used it once, and probably not to full capacity, since I'm still trying to figure out the relative heights of the two tanks (ie if the black tank is higher than the grey, then this will just further fill the grey with the contents of the black).

Before anyone gets excited about the prospect of mixing grey and black - it's no problem for me since we only pee in the trailer.

Anyone know if the two holding tanks are on the same level?

It's a pain that AS makes the classic with a 54 gal fresh tank, and only 39 gal grey. I use very little in the black tank.
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Old 08-09-2015, 05:35 PM   #3
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Doesn't the bunkhouse model have a macerater? I suppose you could, for example, place a small basin in the sink, either kitchen or bathroom, put washwater in it, then dump in the toilet.
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Old 08-09-2015, 06:14 PM   #4
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Doesn't the bunkhouse model have a macerater? I suppose you could, for example, place a small basin in the sink, either kitchen or bathroom, put washwater in it, then dump in the toilet.
Yes the bunkhouse has a macernator

We also do wash dishes in a basin and dump in the toilet.

The issue is that the showers fill the grey and so I'd like to get some that grey already in the tank over to the black tank.

I would probably not go the other way contaminating the grey tank with black water, my assumption is the grey tank and associated plumbing is not suitable for black water.
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Old 08-09-2015, 06:35 PM   #5
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we tend to fill grey faster than black and end up dumping due to full grey but with not so full black.
Isn't that what a Thetford "blue boy" is for? And with a macerator pump, you don't need a giormous blue boy that's the same size as your gray tank, a smaller and easier-to-handle model will do just fine, because you can shut off the macerator pump with the gray tank only partially emptied in order to avoid overfilling the smaller blue boy. It's also a lot easier to take a blue boy to the dump station than it is to take the whole trailer there.
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Old 08-09-2015, 09:06 PM   #6
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I have that tote, Thetford is grey, the blue ones are by Barker Mfg. I actually built a system with 2 totes on a cargo carrier mounted on a front hitch of my truck. I use a Macerator to pump from the tanks up into the totes and go to the dump station. But that is a lot of equipment for a 2-3 day weekend. If I had another 20 gallons of grey capacity I could leave all that behind. That's a big deal if you put together a long trip with a fequent stops. I kind of try to be a minimalist these days from former years of bringing way too much "stuff." It seems silly to me there hasn't been more thought put into maximizing tank efficiency by the manufacturer.
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Old 08-09-2015, 10:12 PM   #7
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Well, Ted... perhaps using paper plates might reduce 'gray water' usage. Also, some modifications in showering in the AS.. commonly referred to as 'Navy Shower'.. but basically wet, soap, rinse... Or, use the local 'showers'.... Another option would be to set up an 'outdoor' shower for the 'big rinse off', then the shower in the AS would be minimal.

We have found that using paper plates when we have no 'sewer connection' at the site really increases our capability.

With that said, I personally would NOT 'mix' the gray/black tank contents. Here is one reason... Imagine, your 'gray' is really full. You then 'move' your AS... and if you 'brake', the contents can slosh toward the bow... then filling up your shower pan with 'cross-mixed' contents... not the best I would think... If your shower pan is behind the gray tank, accelerating or if not level, the contents will seek 'level'...

I would not ask my lovely bride to clean up that mess... and, if it sloshes outside on to the floor, that might be bad.

Good luck figuring out what works for you..
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Old 08-09-2015, 10:13 PM   #8
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Is this when boondocking? Can't you just drain the gray to the ground? Guess not if you're in a camp w/o hookups.
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Old 08-09-2015, 10:30 PM   #9
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Just to be clear, I would never allow black water in the grey tank, only excess grey into the black tank.

This is when dumping greywater on the ground is not permitted.

However, thank you all for your input.
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Old 08-09-2015, 10:35 PM   #10
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Bleeding greywater into black tank

Drain a few gallons from the gray tank into a bucket and dump it into the toilet. That's one way.
If you do a lot of dry camping, you can put a tube down into the gray tank keeping the end well above the bottom of the tank. Connect that tube to the inlet of a second fresh water pump. There should be a valve behind the toilet which allows you to shut off the water to the toilet. Install a "T" fitting between that valve and the toilet. Connect the output from the second pump to that "T". Turn the water supply to the toilet off. Turn the second water pump on. When you flush, the flush water will be drawn from the gray tank to do the job. You can leave the pump turned on if you wish. It will turn on and off when you flush.
You will be saving fresh water and transferring gray water to the black tank.


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Old 08-10-2015, 07:34 AM   #11
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My 78 Trade Wind has separate dump valves for black and grey. I thought they all had that.


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Old 08-10-2015, 08:59 AM   #12
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My 78 Trade Wind has separate dump valves for black and grey. I thought they all had that.
They do. But the dump lines still come together where you attach the slinky, and so it is possible to mix the black and gray water by opening both valves at once with the cap on in place of the slinky.

The problems with that are many. First, water doesn't just flow one direction unless one tank is higher than the otheró it flows both waysó so you not only get gray water into the black tank, but you get black water into the gray tank. The reason is because black water and gray water have different densities due to the chemical compositionó urine and feces are both heavier than plain or soapy water and will settle if not constantly agitated. As gray water flows into the black tank, black water flows out under it, until you have a uniform layer of gray water on top of a uniform layer of black water in both tanks.

Second, you can't get the mixed water back out of the dump lines because they're the low point in the whole system, so even after you close the valves again, as soon as you go to the dump station and take the cap off to connect the slinky, sploosh! A mixture of (mostly) black and (some) gray water all over.

Not to mention that driving to the dump station with the dump lines full of water runs the risk of rupturing those lines because they're not designed to bounce around full of water while in transit. Those lines aren't load-bearing.

Which is why if the OP wants to use his black tank to stretch his graywater capacity, it needs to be done by flushing the toilet with gray water and not by cross-connecting the two tanks by opening both dump valves at once.
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Old 08-10-2015, 09:34 AM   #13
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This is an interesting discussion. Just after buying our trailer about a year and a half ago I read a thread which advocated using gray water to help flush the black tank. As suggested in that thread, when emptying tanks I drain the black tank first, then close the dump valve and open the gray tank valve. After I hear the initial rush of water I close the gray valve and open the dump valve. The inital effluent looks like gray water, indicating to me that the water in the common pipe, and hopefully all the plumbing is, in fact, gray water. After a while (10-15 seconds) I begin to see black tank contents exit the drain. I will do this several times and then as a last step, empty the gray tank which always looks like gray water.

I don't know about the plumbing arrangements, but the bottoms of the tanks are at the same level, as are the pipes from the tanks leading into the dump valve. I would think that the inrush of gray water would push any black tank contents away from the drain outlet as long as the flow was in that direction.

I have not noticed any odor from the shower or sink drains in the trailer. Also, other than concerns about dumping gray water on the ground (which I have never done and probably wouldn't do) how would mixing the contents be any different from the older trailers that do not have gray tanks?

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Old 08-10-2015, 09:53 AM   #14
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A simple thing is being made MUCH too complex. Get a plastic milk jug (1 gallon size), cut the top off, but leave the handle intact. Shower with the plug IN the shower drain. Bail the shower into the toilet using said milk jug. Flush. Repeat. When the water in the shower is so low it's hard to fill the milk jug, pull the plug.
If the black tank reaches the 3/4 full it's time for a trip to the dump station.
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