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Old 08-16-2008, 09:13 PM   #1
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1958 18' "Footer"
Sebastopol , California
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Combining Black and Gray Water

I would like to add a holding tank to my AS. At this time it doesn't have a black or grey tank. I posted earlier asking about a recirulating toilet, not going that route! Is there any other draw backs to having one tank for black and grey water besides lack of capacity? Smells thourgh the pee trap? Anything I'm not thinking of? I have a small AS, 18 footer. No shower, just a sink and a toilet. I can safely fit a 16 gal. tank. 90% of my camping would be done with full hook ups.

Thanks in Advance

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Old 08-16-2008, 09:21 PM   #2
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hi greg...

with a small tanks and no shower, capacity isn't a big issue.

mixing sink water into the black soup can alter the normal digestive process...

that is supposed to happen in a healthy black tank.

it is probably a minor issue in this case.

otoh, with full hookups, u will still need to keep the drain valve closed most of the time...

so enough fluid accumulates IN the tank to move the poop through.

with separate draining lines the wash water can be mostly left open when hooked up...

that become a very bad idea on the black tank side.

if not planning to boondock, dumping wash water (where permitted) isn't an issue.

yes the sink traps can leak odors as the water seal evaporates.


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Old 08-16-2008, 09:23 PM   #3
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Our friends have an 04' Safari with a combine 70 gal gray and black tank.. They like it. Makes life easy... It is located just rear of the axels, maybe part under them...

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Old 08-16-2008, 09:26 PM   #4
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The only issue I could see is that you could not dump the gray on the ground (it is legal some places) if you were on an extended boondock. Since you have no shower your gray water would be minimum. As long as you have water in the P-trap, you should have no odor backing up.


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Old 08-17-2008, 05:45 AM   #5
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I added the kitchen sink water to the black tank in our Overlander. The bathtub and bathroom sink water are not as nasty as the stuff coming out of the kitchen and toilet.
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Old 08-17-2008, 08:03 AM   #6
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It seems like a great deal of trouble to basically replumb, refit and make sure everything drains and vents properly. We do not have a gray tank but use a mobile blue tank instead and have found it very easy to use. We looked into adding a gray tank but could not find ample space for one large enough to make it worthwhile. If you are only planning to boondock occassionally I would consider the blue tank. Just my opinion. Good Luck!

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Old 08-17-2008, 09:06 AM   #7
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Combined tanks are a love it or hate it type relationship for most. I don't care for them due to the way I camp, mostly boondocking and non-hookups.

The factory did the combo tank and then quickly retreated from it.

The main factor as I see it is that if you use the shower, it is the single largest use of water. If you do not go to places with full hookups or at least sewer hookup, the issue is compounded because now say yer in a state forest campground or a place where you normally could let your gray water out, you can't do that when it's mixed with raw sewage.

If you typically go to places with a least sewer hookup and/or don't use the shower that freq, then you should be fine.

I have a 39 gal fresh tank and a 39 gal separate gray tank. Using the shower conservatively, I was able to squeeze 4 days out of it with two people. My black tank is only 18 gallons. Having it separate has allowed me to not fill the black tank with 3 campers for well over a week. In these cases I'm in a state forest campground in the middle of nowhere and buy about 10-20 gallons of 2.5 gallon jugs at the local store to continue to fill the fresh tank as needed (since town is 30 miles one way). As you can imagine, if I had a combined tank, I'd be in some trouble because I can at this place dump my gray tank. There are no dump facilities at this rustic campground for my black tank, so in this case, having the dual tanks works very well.

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