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Old 09-10-2011, 09:38 AM   #1
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Toronto , Ontario
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Convert black tank to grey?


I have a 73 Overlander with a rear bath that I am gutting and modernizing. I would like to add a grey water system, and had a bit of an idea this morning.

Since we will be re-configuring the entire trailer, would this scenario be possible:

Leave the existing black water tank in place on the rear street side of the trailer. Make the black tank my new grey tank, and move the shower to the street side.

Add a new above-floor black tank on the curb side and a new low-height toilet to dump directly into the new tank.

This would eliminate dropping the belly, ripping up the subfloor (which is in excellent condition), etc.

Would the capacity of the old black tank be adequate for use as a grey water system? I could run my new drain entrance plumbing under the new shower base. I just can't find the black tank capacity information anywhere.

Ideas, ideas...

thanks -Jamie

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Old 09-10-2011, 10:06 AM   #2
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Do you know the dimensions of the tank?

If you do, then take the total cubic inches and divide by 231 for gallons. That will give you an approximate answer since most tank dimensions are for the outside of the tank, and wall thickness take some of that away. Plus, you have the drain pipe from the tank to the dump valve, which adds capacity.

If you don't know the dimensions, one way to figure it out would be to start dumping gallons of water into the tank, one gallon at a time, until it's full. Plastic 1 gal milk jugs would work. Might take a bit of time, but you'll have an accurate answer.


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Old 09-10-2011, 10:50 AM   #3
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How are you planning the dump system for the new black tank?
"If it can't be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled or composted
then it should be restricted, redesigned or removed from production."
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Old 09-10-2011, 01:05 PM   #4
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Toronto , Ontario
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I was thinking of connecting to the main sewer connection through some of the existing holes in the floor from the old shower, etc.

I don't have access to see the size of the tank. I bought the trailer, which hasn't been used in 15 years and have it parked in a utility yard right now, and in the process of tearing it apart realized that the previous owner has left me a 15 year old full tank of presents...

so now I have to find somewhere in downtown toronto to dump a trailer tank...a heavy task (pun intended...)
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Old 09-10-2011, 01:58 PM   #5
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There are no mechanical reasons why you can't change the use of the black water tank.

You want to consider that your new tank has a 3 in. drain line and not rely on the old 1 1/2 in. shower drain.

Most homes have a sewer clean out at the curb.That is what I use to dump many times when there is a line in the camp ground.

In all likely hood the floor will have to come up or the pan down to run the larger sewer line so plan with that in mind and you may not have to use a special toilet.

Another trick I have used is to connect the tanks with a small pipe from the bottom of the gray tank to the top of the black tank. Excess gray water just flows over to the black tank and extends things on a long weekend. Starting with a small tank on the gray side makes this a useful consideration.
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Old 09-10-2011, 02:18 PM   #6
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Hi Jamie welcome to the forums from a fellow Ontarian. I'm a couple of hours north west of the big smoke.
The first problem I can see is capacity. The black tank in your trailer is probably 12 gals. That would be way too small for a grey tank. One shower and the tank will be full. Even as a black tank it is too small to be of any practical use. Airstream never published tank capacities from back in the 70's. They simply state the tank size as "about one weeks" capacity. Boy were they wrong on that estimate.
I think as long as your getting in to it the best way would be to drop the belly and replace the black tank with a larger one and add a grey tank or two which will give you adequete storage capacity for normal use. You can then easily replumb the imput to the tanks and the outlet drain system.
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Old 09-10-2011, 03:07 PM   #7
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Black tanks are without an elbow, toilet dumps straight in using the valve to seal off gases, grey tanks use water sealing elbow. My grey tank is twice the size of the black and it is the limiting factor for length of time before dumping. Make sure you consider where the vent stack will go from a new black tank.
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Old 09-10-2011, 09:03 PM   #8
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Our black tank in a '72 Sovereign is an 18 gal. You might get lucky with the undumped black tank as we were - it was all composted black liquid without any odor when we discovered it and dumped. If the liquid evaporated or leaked, you'll have cement. Might take awhile to soften up to dump. Grey tanks usually are at least twice the capacity of the black tank. We never have to dump because the black tank is full, it's always the grey that fills up first.

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Old 09-10-2011, 09:17 PM   #9
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Hey,we just remembered that we have our old black water tank. Its still watertight and in good shape. 18 gal with a rear outlet. Free to a good home - you pay shipping...
oops- posted in wrong thread. Not sure how to delete.

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