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Old 01-15-2016, 02:26 PM   #1
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1976 25' Caravanner
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How Should I Dump? (Gray tank only)

During a planned shell-off renovation I intend to reconfigure tanks and plumbing with the intent of increasing fresh and gray water capacity while eliminating the black tank in favor of a composting toilet. The primary use of this trailer is aimed at full-time, mostly boondocking/dry camping. While I have plenty of experience backpacking/tent camping I am admittedly new to the concept of camping with 5th avenue on wheels so bear with me...

I make good use of the search function and have found tons of useful info on tank design, plumbing, and even extensive discussions about the appropriate disposal of gray water. But I have not come across any specific topic that addresses my situation.

One of the apparent advantages of ditching the black tank, at least on the surface, is that I can get rid of the stinky slinky, simplify plumbing, and cut ties to dump stations and everything that goes along with them. But...I still have a tank of water to dispose of. Also, I am aware that some amount of food solids, hair, etc. will find its way into the gray tank and therefore will require a valve and hose that are sized accordingly. However, I would like to minimize the size and complexity of the drain plumbing.

Here are my questions:
(1a) Am I still mostly relegated to finding dump stations?
(1b) If so, do I still need the big 3" hose and fitting that interfaces with the "dump hole"?
(1c) If I don't need the 3" hose and gate valve then how small can I go? Still needs to be a gate valve?
(2) Are there other locations where you can dispose of large quantities of gray water?

Any input appreciated, thanks!

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Old 01-15-2016, 02:48 PM   #2
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I think it would be safe to say that many, if not most of the places you would likely be boondocking do not want grey water on the ground so, yes, you need to be able to use dump stations. I would think that a standard 3" dump hookup is best in terms of resale (someday) and it will minimize the time you spend dumping. Not to mention that the pipe and fittings are readily available.

In the arid Southwest, there are many places that are exceptions to this generalization and folks use a Valterra to garden hose adapter and run their gray water into a "gopher hole".

I know that grey water seems harmless -- some soap, some dirt, some food particles, but a few years ago one of the major magazines (Airstream Life ???) ran some through a bio lab and it turned out to almost as toxic as black water... I sure wouldn't want it dumped near my house (our water table is about 8' down).

Just my 2 cents,


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Old 01-15-2016, 03:33 PM   #3
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Originally Posted by Mr.Anderson View Post
(1a) Am I still mostly relegated to finding dump stations?
That will depend on where you camp. Some places allow direct discharge of gray water; some do not.
(1b) If so, do I still need the big 3" hose and fitting that interfaces with the "dump hole"?
No— but see next answer. Also, some places will require a gas-tight seal to their sewer hookup to control odors, so you may need a fitting. You can make your own from a PVC pipe end cap drilled for whatever hose size you use.
(1c) If I don't need the 3" hose and gate valve then how small can I go?
You can determine that if you have a background in engineering, specifically hydraulics. The hydraulic head in feet is the vertical distance from the water surface in the tank to the end of the hose. One foot of head is 0.43psi, but for ease of illustration and because I don't know the height of your tank I'll say you've only got 1psi pushing the water out of the gray tank. It's open-end discharge, meaning the outlet of the hose is open to the air, not underwater, so the pressure at the outlet end of the hose is 0.00psi. Based on these values, a 3/4" hose will give you a discharge rate of about 5 gallons per minute for a 25' hose. Actually a little less because there's additional head loss through hose connectors, but we'll ignore that complication for now.

If you go with a 3" hose instead, under the same conditions (1psi, open-end discharge), your flow rate goes up to a whopping 200 gallons per minute through a 25' hose, and dumping your gray tank will take mere seconds from the time you open the valve. A slinky doesn't have the same smooth walls as a garden hose, so there are additional head losses per foot, but we'll ignore that complication for now, too.

So to answer your question, hose size determines the time it takes to dump the tank, and going smaller is fine if you don't mind waiting longer to finish dumping.
Still needs to be a gate valve?
A valve is a valve is a valve. They all do the same thing. There are advantages to a gate valve for this application, though. The valve is very flat and takes up little room. It operates on a simple push/pull so it's easy to locate the operating handle well away from the valve itself and you don't have to crawl underneath the trailer to work the valve.
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Old 01-15-2016, 07:22 PM   #4
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I dump gray water through a 3/4" hose with no problems. Saves having to store and play with the stinky slinky. Takes a little longer but I've never held anyone up.
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Old 01-16-2016, 05:38 AM   #5
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i agee, a garden hose can be use in place of the three inch thing. Just get an adapter with a hose fitting. Should still be dumped into a dump station, tnough.
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Old 01-16-2016, 12:33 PM   #6
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Grey water disposal

If it were me I'd give serious thought to installing a macerator system. That gives you the advantage of even dumping upslope from your rig. Also eliminates the need for a bulky stinky slinky hose. It will cost a little more up front, but I think you'll be glad you did.
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Old 01-16-2016, 01:26 PM   #7
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RV Macerator Pump & RV Waste Disposal Accessories
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Old 01-18-2016, 02:58 PM   #8
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Thanks all for the helpful info. Sounds like I have options!
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Old 01-18-2016, 03:55 PM   #9
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One last thing that I didn't see mentioned above is the cap adapter (if mentioned forgive the repetition). Available at Walmart this thing reduces the 3" hose for draining with a cap that attaches bayonet style to your trailer outlet & has a garden hose connection so when you find yourself in an area that grey dumping "might" be appropriate you can attach a small hose for slow discharge.
Regarding your original question the 3" piping is without a doubt the best option for draining at a dump station.
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Old 01-18-2016, 04:24 PM   #10
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You CAN also use a Sewer Solution - Look it up in camping World. It does allow you to backflush your tank(s) if they get really icky. I find that dumping a big kitchen sink full of very hot water into the gray tank can dislodge a significant amount of stuff you don't think about - hair, soap scum, kitchen grease - into the hose.


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