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Old 03-21-2016, 10:28 PM   #1
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1972 27' Overlander
Templeton , California
Join Date: Oct 2015
Posts: 6
Fresh water to grey water in Overlander

1972 27' Overlander Twin

I'm assuming a tank is a tank.? I'd like to move my rear bath to mid trailer but of course the biggest issue there would be drainage. Since the existing fresh water tank would only be a few ribs away, is there a reason why it wouldn't work? Fresh water storage could always be added above the floor.

One big benefit of this arrangement would be taking some weight off of the rear of the trailer by removing the original black water tank. This would help alleviate the rear end separation issue with these models.

Has anyone done this yet?

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Old 03-21-2016, 11:09 PM   #2
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2012 Interstate Coach
Metairie , Louisiana
Join Date: Dec 2011
Posts: 9,085
Originally Posted by ryry View Post
Since the existing fresh water tank would only be a few ribs away, is there a reason why it wouldn't work?
Let's see…
  • The existing fresh tank doesn't have a dump valve.
  • When you add a dump valve, the existing vent will be too small; it needs to be large enough to let air in as fast as the water flows out. But you might repurpose the existing fresh tank fill to serve as a vent, with a modest amount of work, including extending and rerouting it through the roof; you could leave it where it is, but then you might have an ongoing odor problem. Through the roof is better.
  • Also when you add the dump valve, you have to make sure the dump valve exits forward or rearward of your wheels; a fill port could be over the wheel well, but a dump valve can't. I don't know exactly where the fresh tank is on your particular trailer, so that may or may not be an issue for you.
  • Wherever you move the new fresh tank, you'll need a wall penetration for a new fresh tank fill.
  • You will also need to provide additional support for the new fresh tank.
  • You'll also need to relocate the fresh water pump so that you minimize the amount of suction needed to self-prime.
  • You may also need to relocate your municipal water intake, or at least run a new pipe from the existing fill to the new tank so it can be teed in near the relocated pump.
  • You will alter the balance on the trailer. Moving the rear bath forward adds tongue weight because the whole center of gravity shifts forward.
  • You may even end up altering the weight distribution on your trailer tires. Under ideal loading condition, if you were to put scales under all four wheels, then the load on each wheel should be almost the same. By shifting the bathroom weight and gray tank weight forward, you're adding load to the front wheels and taking it off the rear wheels. Which will have an effect on tire wear as well as braking effort per wheel.
None of these points is insurmountable. You could do it. But I guess the point I'm trying to make is, you can't look at the tank location in isolation, but instead have to look at it as part of the overall system. If you're committed to relocating the bathroom, then putting a gray tank where the fresh tank is now is as good a place as any, as long as you keep the other points in mind.
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