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Author Topic: Utilizing Black Tank for Gray Water Overage  (Read 688 times)
sailors35
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« on: February 20, 2018, 02:11:54 pm »

What is this best procedure for doing this?  Does it work and how well? 

Many thanks
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« Reply #1 on: February 20, 2018, 03:29:32 pm »

Hi Sailers35,

Yes it works very well.  We have practiced it often for 10 years with our PC.  The procedure is as follows.

- open gray tank valve (this floods the drain pipes right up to the black tank valve)
- open black tank valve (the deeper gray water will rush into the shallow black water inside the black tank)
- close black tank valve after 15 to 20 seconds
- close gray tank valve

This process is not just good for extending your time between dumps, but flooding gray water into the black tank helps to clean out the black tank at dump-time.

I am making a modification with our 2350, adding duplicate dump-valve switches inside our bathroom inside the vanity base cabinet.  This will allow us to blend the tanks from inside our PC which is most often needed during our shower time.
« Last Edit: February 20, 2018, 03:36:24 pm by ron.dittmer » Logged

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« Reply #2 on: February 20, 2018, 03:45:34 pm »

Quote
I am making a modification with our 2350, adding duplicate dump-valve switches inside our bathroom inside the vanity base cabinet.  This will allow us to blend the tanks from inside our PC which is most often needed during our shower time.
Hey, Ron please post the info on this when you get done.  It's on my list to do as well.  Including a switch for the macerator pump.
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« Reply #3 on: February 20, 2018, 06:47:46 pm »

A few questions to those of you that use the gravity flushing of the grey tank to the black tank as Ron described above:

Can you actually fill the entire black tank with this process?

Why are you NOT concerned about cross contamination of gases and fluids between the two systems?

Doug


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« Reply #4 on: February 20, 2018, 07:27:47 pm »

A few questions to those of you that use the gravity flushing of the grey tank to the black tank as Ron described above:

Can you actually fill the entire black tank with this process?

Why are you NOT concerned about cross contamination of gases and fluids between the two systems?

Doug
My experience with the blending of tanks is that when we do it, it is almost always done one time between dumps.  Very rarely have we done it twice.  By that time, we are nearly completely out of fresh water of which we try hard not to wait that long.

It has been extremely rare when in a situation where we have campsite water but not a dump.  I recall only one time where we carried both a full tank of fresh water along with significant waste water also on-board.  Usually when fresh water is available but a dump is not, when permitted by campground rules, we slowly release gray water into adjacent woods instead of blending tanks.  That buys a lot more time before requiring to dump.

Concerning back-washing black water into the gray waste system, I am sure it is possible but is surely very limited.  I can't imagine it backing up through the gray waste pipes all the way to the shower pan where it would present a problem.  Still I see your concern.  If you want to play it most safe, I recommend blending the tanks only once between dumps.
« Last Edit: February 20, 2018, 07:34:42 pm by ron.dittmer » Logged

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« Reply #5 on: February 20, 2018, 07:37:07 pm »

Quote
Can you actually fill the entire black tank with this process?

Why are you NOT concerned about cross contamination of gases and fluids between the two systems?
Completely fill? I doubt it.  Once the levels are equal flow from the gray to the black stops.  So unless you are going to continue running water into the gray tank with both valves open, No.  Theoretically I guess you could as a test.  I would strongly suggest not trying that.  If you follow Ron's directions and use the trick once between dumps you should not have any issues.

If you shut the gray valve first as Ron explained cross contamination is unlikely as flow out of the gray tank is still going.  I guess you could if your black tank was already higher than the gray tank but in that case you already have problems enough and should be dumping not transferring tank to tank.

As to cross contamination, what is the concern?  Both tanks dump into the sewer.  All drains have traps on them so no gasses are going to come up from either tank.  I don't understand what the issue is.  Everything in my house ends up in the same septic tank.
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« Reply #6 on: February 23, 2018, 12:25:06 am »

I was hoping that there were others out there that would chime in on this subject. I suspect that most PC owners do not spend much time away from the pedestal. It appears there is not much interest in this subject.

Im sure somewhere it has been posted as to what happens when you do not manage your waste waters, but it might help to review the potential situations.
These are my experiences over the years with several RVs, this is not PC specific, but it applies.
 
Our primary use is to spend as much time away from the pedestal as possible. The only two limiting factors, for us, are the time we can devote to a trip, and potable water.
Potable water needs to go somewhere, black or grey, until you can find an appropriate place to dump. So this means you have to have tank capacity, and the ability to get the waste there. Hence Sailor 35 question    What is the best procedure?

On many RV models, like the PC 2350, and other PC models, the waste tank capacities require you have a plan. What happens when your grey tank gets full? Generally it will back up into the shower, it has to go somewhere. If you are taking a shower and it backs up, you are instantly reminded of everything you have put down the kitchen sink because it is floating around your ankles. Another experience with a full grey tank will have you mopping up the shower, and sometimes the floor in the bathroom area when waste water sloshes out of the shower drain pan driving down a windy road. Both situations can be avoided, but they have to be managed.
 
This is why I respectively disagree with JaTrax comment comparing a house sewer, or house septic system to an Rv system, as being the same.. Sewer and septic are what I would describe as an OPEN system, meaning  basically it all runs downhill until its gone, versus an Rv system that I would call a Closed system, that needs to be managed, and doesnt run anywhere except to a tank, shower, sink, etc. unless you are Hooked to a sewer with open lines.
 RV builders have made a point, for decades, of seperating the grey from the black, my experience is limited but I have never heard of any Manufacturer(except PC)  suggest comingleing grey waste water with black, being  acceptable. This is the process Ron has described above.
If you have two tanks both with fluids and open valves connecting them, anything can happen.

So, what it comes down to is a choice, like so many in life, what is the gain, and what does it cost? From what I can determine, relying on Rons posts, gravity blending the tanks will allow you to dump your grey tank 1x into the black tank. On a 2350 with a +/- 23 gal grey tank, I suspect that will amount to maybe 18 gals. Im taking into consideration you do not ever want to fill your grey tank full to start with, and with this gravity equalization process you will never want to completely drain the grey tank. I think 18 gals would be generous based on the fact you will be guessing as to when to shut the grey tank off, and that is critical. The gain 18 gals. The cost, in my mind is potentially contaminating my grey system, with black waste.

For me, I have problems dealing with peas floating around in my shower, I know I dont want any chance of TP. So the gravity, equalization transfer of 18gals from the grey tank to black tank will Never happen for me.

 I will be the first to acknowledge, these are probably extreme ends of the spectrum. But, this is reality, and something that can happen, and something you should be aware of so you can make an informed decision.

I will be carrying extra potable water ,beyond the factory supplied capacities, and needing to fill every possible place I can find with waste water.

Which brings me back to the original question, what is the best procedure?
Doug
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« Reply #7 on: February 23, 2018, 05:12:01 am »

I know some people use their outside shower when boondocking. If you aren't far enough off the beaten path to avoid startling people, they sell pop-up shower/changing stalls. I would recommend biodegradable soap like we've used on wilderness trips. No water is going into your tanks.

John and I also do"bucket baths" after which the wash water dumps into the toilet. Those little hospital wash bins fit right down in the bottom of the bathroom vanity. Our spillable bath products ride in them just in case.

And for in between clean, alcohol free wet wipes do the trick.

I'm pretty sure a good many people on this forum dry camp (Ron D included) and with water management and conservation, it can be done comfortably. Our longest with no hook up and no dump was ten days with two people on board.
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« Reply #8 on: February 23, 2018, 08:22:12 am »

A solution to back flow into the shower when the gray tank is full is to replace the P trap with a Hepvo valve http://hepvo.com/

These are commonly used and have a proven track record.  I used one for several years in another RV with good success.  Another advantage they do not require antifreeze for winter storage. On the previous unit it was originally equipped with a P trap and a manual gate valve to prevent back flow into the shower pan.  The Hepvo valve allowed replacement of both. I have not installed the Hepvo unit on the PC but I would expect replacement of the sink P traps to be relatively simple whereas the shower would be another matter.  In hind sight I wish I had Phoenix install Hepvo units in all locations during the initial build.  
« Last Edit: February 23, 2018, 09:04:47 am by fandj » Logged
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« Reply #9 on: February 23, 2018, 10:13:33 am »

We don't dry camp that much but when we do,  I routinely release some of the gray into the black,  but like Ron said,  one time only.      I  listen for the rush  of gray to black to subside,  then close
the gray valve, followed by the black valve.    That way I feel confident no mixing has occurred.   
I do the same when dumping, opening the gray valve after the black has drained, allowing gray to flow into the black tank to "rinse" it,  closing  the gray valve and re-dumping the black.    Leaving some gray water in the tank,  I then drain that.
Seems to work well.
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« Reply #10 on: February 25, 2018, 06:23:15 pm »

Has anyone ever tried plumbing  a "T" on the discharge side of the sanicon and plumb it directly into the black tank so you could pump from the grey to the black?

Has anyone got desperate and fished the sanicon hose through the bathroom window and pump the grey tank into the toilet?

Doug
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« Reply #11 on: February 26, 2018, 07:50:35 am »

Has anyone got desperate and fished the sanicon hose through the bathroom window and pump the grey tank into the toilet?

Doug
That is an interesting thought of which I never considered.  Not only would it prevent any potential for black water into the gray tank and plumbing, but theoretically you could empty the entire gray tank into the black tank.

Still, blending the tanks as we practice has been clean to operate, convenient to do, and solves the problem with a full gray tank.

I do think the concern of contamination from the black tank into the gray tank is not warranted as long as you....
- follow the proper sequence
- listen for the water flow
- and close both tank valves immediately after its get quiet.

There is a buffer of pipe between each tank valve.  If there was any backwash contamination, it would be trapped in the pipe between tank valves.
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« Reply #12 on: February 26, 2018, 03:16:45 pm »

In some models like the 2552, the gray is bigger than the black. You could. Overflow the black.
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« Reply #13 on: February 26, 2018, 04:31:38 pm »

Wrong Tom. Gray is smaller on 2551 & 2552.

And water seeks its own level so the tanks will be the same water height in any case.
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« Reply #14 on: February 26, 2018, 04:47:40 pm »

Wrong Ron. Gray is smaller on 2551 & 2552
  Did you mean Tom?
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