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Old 10-23-2016, 11:56 PM   #1
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Cool Use Black Water Tank as Aux Fresh Water Tank?

We are planning to custom build a brand new 25' AS. As part of this, we plan to replace the stock toilet with a Separett Composting Toilet.

As you probably know, the Separett diverts urine and solid waste into two separate waste streams. The solids are stored in a vented compost bin while urine is drained to a separate holding tank/bottle.

The current 25' AS waste system combines all the toilet waste and directs it to the black water tank. The bathroom sink is also directed to the black water tank.

The waste streams from the galley sink and the shower are directed to the grey water tank.

Because, some human waste from the galley sink and/or the shower will always end up in the grey water tank, is it ok to divert the bathroom sink waste water to the same grey water tank?

AND, because of the dilution effect of all these waste streams ending in the grey water tank, is it ok to divert the urine stream from the Separett to the same grey water tank?

ALL the AS waste streams, except the toilet solids, would now be held in the grey water tank, converting the original grey water tank into the new black water tank.

With this waste disposal arrangement, the original, brand new, black water tank should now be free of human waste, and could be used as an auxiliary fresh water tank.

Do you think a brand new AS 25' plumbing system could be rearranged to accommodate a repurposing such as this?

I know this design may cause some concerns .

However, an extra 37 gallons of fresh water would come in handy for an extended boon docking adventure.

Please let us know if this idea is feasible?
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Old 10-24-2016, 03:27 AM   #2
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I would look at what you are going to do with the extra fresh water. If you convert the black tank into an auxiliary fresh water tank you will have about 75 gallons of fresh water on board, but only about 35 gallons of grey water storage.

You'll need a place to put the extra 35-40 gallons of water when you are done with it. If you plan to "gopher hole" it, consider that it also contains your urine stream so it's not really graywater, it more like yellow graywater.

This may not be a problem where you plan to boondock. I would leave the blackwater tank as an auxiliary graywater tank, and bring the additional freshwater in jugs.
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Old 10-24-2016, 05:16 AM   #3
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Unless someone at the factory, or the person delivering the Airstream, had an emergency and used the toilet...
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Old 10-24-2016, 05:49 AM   #4
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Even a new black tank may not be suitable for drinking water depending on the material used to build it. There are lots of containers suitable to carry extra water in the tv or in the trailer. Easy to carry an extra ten gallons or so.
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Old 10-24-2016, 05:58 AM   #5
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You will no longer have a gray tank, it will be a black tank. Disposal of this waste is more involved than just dumping the grayvwater somewhere. If you pee in the shower, that's black water, so your gray tank us now a black tank. If you wash off between yor legs, etc at the bath sink and rinse the cloth, that makes it black water. So I think what you want to do will work as long as you know that it all will be black water and disposed of properly.
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Old 10-24-2016, 12:52 PM   #6
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What we do...we switch depending on need. We usually use the blackwater tank for its stated purpose, but use it for drinking water storage when we boondock in between. It saved us the (probably) considerable investment redoing all the existing plumbing as you suggest, while giving us the 75 gal drinking water when we need it. This approach also seems to keep the black water tank cleaner.
Safe travels. jon



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Old 10-24-2016, 02:01 PM   #7
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^ good one B00merang, you had me going for a second there.
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Old 10-24-2016, 02:08 PM   #8
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The 37 additional gallons of water weighs in at 314 pound fyi.
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Old 10-24-2016, 02:11 PM   #9
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A lousy idea all-around in my personal opinion.

Con's >>>>>> Pro's

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Old 10-24-2016, 05:40 PM   #10
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If you think carefully and remove any chance of cross connection, and the black tank is made of suitable material it would work. It's not something that I would do though. It might have a negative impact on the resale value of the trailer and carrying extra weight in that location might not be the best place. It might be more user friendly to carry the water in containers and have the extra waste water capacity? Depends on how you will use the trailer I guess.
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Old 10-24-2016, 05:55 PM   #11
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Note that many if not most AS bathroom sinks already drain to the gray tank. My US-model 2013 25FB is this way. Of course I've never seen an Oz-spec trailer.

When you say "custom build" do you mean you are going to buy a retail trailer and gut it, or are you buying an empty shell?
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Old 10-24-2016, 06:13 PM   #12
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I would think it would be much simpler to just add another freshwater tank. Set if forward of the axle like they were in earlier years.
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Old 10-24-2016, 06:47 PM   #13
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In our 75 Overlander all grey water goes to the grey tank, and only the toilet goes to the black tank.

Go spend a little time talking to your local county health authority about your idea. Also go to a waste water treatment plant and see what happens to it. There could be a reason why human waste (urine and feces) is handled differently from the water we wash our bodies and dishes with ...
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Old 10-24-2016, 08:07 PM   #14
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Quote:
Originally Posted by B00merang View Post
What we do...we switch depending on need. We usually use the blackwater tank for its stated purpose, but use it for drinking water storage when we boondock in between. It saved us the (probably) considerable investment redoing all the existing plumbing as you suggest, while giving us the 75 gal drinking water when we need it. This approach also seems to keep the black water tank cleaner.
Safe travels. jon



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Old 10-24-2016, 08:16 PM   #15
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Using a black tank for fresh water is not the best or safest idea.
I would only use containers made for fresh water. Get a fresh water tank for goodness sake.
The plumbing to the drain valve is to close to the gray, now black. Cross contamination issue waiting to happen

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Old 10-24-2016, 08:19 PM   #16
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Quote:
Originally Posted by nrgtrakr View Post
In our 75 Overlander all grey water goes to the grey tank, and only the toilet goes to the black tank.

Go spend a little time talking to your local county health authority about your idea. Also go to a waste water treatment plant and see what happens to it. There could be a reason why human waste (urine and feces) is handled differently from the water we wash our bodies and dishes with ...
My 2015 25' FC also drained the bathroom sink into the gray tank, like normal RVs.
Which meant that my black tank would last me for the whole 4 or 5 days, before dumping, and flushing.
Then I traded the 25'er for the 30'er, and found that some 'Idiot Child' at AIRSTREAM had tied the sink drain into the black tank.
Now; I need to dump it every two or three days; which in a 'campspot' with no sewage, means that I must disconnect and move to the dump station, then go back and reconnect. A useless hassle.
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Old 10-24-2016, 08:50 PM   #17
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MelGoddard - something like this could at least keep you from having to disconnect to dump.

https://www.amazon.com/Thetford-4051.../dp/B000OR18HS
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Old 10-24-2016, 09:27 PM   #18
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not sure about your area but in our area all water in drains from toilets, showers, dishwasher, washing machine goes out the same pipe to larger pipe in street to the treatment center. so there is no difference between human waste water and dishwasher water in the processing plant.

a gallon of two of urine in some 50 gallons of gray water i wouild guess is not a big deal if released in a good area of ground cover at a rate that allow for absorption vs flooding the area. that is not what i would consider black or sewage water.

Quote:
Originally Posted by nrgtrakr View Post
In our 75 Overlander all grey water goes to the grey tank, and only the toilet goes to the black tank.

Go spend a little time talking to your local county health authority about your idea. Also go to a waste water treatment plant and see what happens to it. There could be a reason why human waste (urine and feces) is handled differently from the water we wash our bodies and dishes with ...
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Old 10-26-2016, 01:31 AM   #19
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Smile Thanks!

Thank you for you constructive criticism!

Based on your feedback to our controversial question , we plan to proceed thusly:

The best use for our Blackwater Tank is as a holding tank for the separated urine stream and the bathroom sink drain stream.

If needed, this Blackwater Tank could also be used as auxiliary holding tank for excess Greywater from the galley sink and the shower.

The best way to have extra Freshwater for extended boondocking is to bring it with you in a separate tank that is specifically designed to store Freshwater.

No mess, no fuss. No difficult piping changes. And, best of all the healthiest way to go.

Thanks, again. This forum is the best !!!
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Old 10-26-2016, 05:54 AM   #20
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If think you have it figured out, good choices.
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