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Old 10-24-2013, 07:01 PM   #1
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1969 21' Globetrotter
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another black tank plumbing question

I previously asked about the placement of the black tank - if it could be in a different location from the toilet. I got a reasoned response that it should be under the toilet because the solids don't need as much water to make it to the tank. Make's perfect sense.

But it leads to another question. If the black tank is on the curb side, or in this case about halfway from center to curbside, and the valve is on the road side, what is the composition of the parts from the tank to the dump valve? It would appear that its just an elbow from tank to pipe, and then pipe to slide valve. It seems to me that the pipe from the tank to the dump valve fills up first, kind of additional holding volume. But it also seems to me that this may create blockage. Or is a system not as simple as described? Am I missing something/misunderstand how it works?
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Old 10-24-2013, 08:18 PM   #2
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Is your tank under the floor
We are facing a similar issue (questions) with our Caravel. Also considering combining the grey water tank with the black water as it seems to be done this way with the new Airstreams. Need to figure out how they get away with this.
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Old 10-24-2013, 09:22 PM   #3
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No, our airstream has no floor right now. Originally it had a black tank above the floor.
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Old 10-25-2013, 06:47 AM   #4
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Quote:
Originally Posted by type901 View Post
I previously asked about the placement of the black tank - if it could be in a different location from the toilet. I got a reasoned response that it should be under the toilet because the solids don't need as much water to make it to the tank. Make's perfect sense.

But it leads to another question. If the black tank is on the curb side, or in this case about halfway from center to curbside, and the valve is on the road side, what is the composition of the parts from the tank to the dump valve? It would appear that its just an elbow from tank to pipe, and then pipe to slide valve. It seems to me that the pipe from the tank to the dump valve fills up first, kind of additional holding volume. But it also seems to me that this may create blockage. Or is a system not as simple as described? Am I missing something/misunderstand how it works?
The valve would be right where the tank outlet is located. If you use T-handles to operate the valve, there would be a push-pull cable running from the T-handle to the valve. Because the valve is at the tank, the pipe or hose (I'll call it a pipe for now) in between the tank and the slinky isn't always full and solids don't get a chance to clog the pipe.

When you first open the valve, the water rushes out of the tank into the pipe, carrying the solids with it. (Side note, if your black tank isn't full when you want to empty it, top it off with water before emptying; it will empty better.) The black water keeps right on going from the pipe to the slinky, and doesn't collect in the pipe. Assuming you've designed and installed it correctly so there's a slope all the way from the black tank to the fitting where you attach the slinky.

Your gray tank should connect to the same pipe at a "Y" fitting, so you only have to connect your slinky once, not move it from one tank to the other. Gray tank would have the same valve setup, a valve right at the tank outlet operated by a push-pull cable. Because graywater contains a lower proportion of solids (hopefully nothing more than small food particles that get past your sink strainer) you don't need as much slope to ensure adequate drainage in the discharge pipe; another reason above-the-floor black tanks are preferred, while below-the-floor gray tanks are the norm.
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Old 10-25-2013, 12:05 PM   #5
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I'm also converting to a curb side wet bath on my 71 GT, but my tank is going to be above the floor with a cable operated valve on the bottom of the tank with piping running down the curb side, with an sweep elbow in the rear frame bay and exiting at the original location on the street side rear. The new ganged together grey tanks will also have a cable operated valve at the exit of the last tank which will be "Y'ed" into the larger black tank piping prior to the exit point. Prior to the dump connection I will install a third manual operated gate valve as a redundent valve in the event either of the cable operated valves fail open or leak, allowing repairs at a better time and place.
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Old 10-25-2013, 04:35 PM   #6
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I am considering using this product for my wet bath, but I am concerned that the tank is pretty small. Pelland Enterprises Motor Home Products - RV Windows
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Old 10-26-2013, 10:58 AM   #7
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Thats tank is only about 9.7 gal. which is awfully small. Another thing to consider is where the outlets exit, as you have the frame to consider. Finding a premade pan plus holding tank is going to be difficult. I looked also but it just wasn't out there. I settled for a ABS holding tank that will protrude underneath my fridge that will be forward of the wet bath and aft of the door. I just couldn't find a anything premade that would fit in the tight space I had to work with. I believe the tank I have is around 15.5 gals.
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