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Old 09-08-2015, 05:01 PM   #1
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Has anyone tried this?

I was reading a post on emptying gw tanks and I thought of this. If you emptied your bw, put the cap back on, and opened all 3 valves would the gw tanks fill the bw tank and kind of give it a rinse? I know you would want a bayonet valve to eliminate a mess but would this work?
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Old 09-08-2015, 05:33 PM   #2
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Just a thought, I think you would stand a good chance of getting some of that junk from your BW into your GW tank/tanks.
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Old 09-08-2015, 06:17 PM   #3
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Good point.
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Old 09-08-2015, 07:21 PM   #4
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But if you parked with the grey water uphill, would it work!?! Hummm
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Old 09-09-2015, 08:06 AM   #5
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On our last rig I had a bayonet valve on the outlet and I actually tried that. It doesn't work as well as you may think. It hardly gets any water into the black tank unless your grey tank(s) are completely full.

I won't say that it doesn't work at all, but a tank flush works much better and is actually faster than trying to rinse the BWT with GW.
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Old 09-09-2015, 08:24 AM   #6
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I do this occasionally when dry camping.

I installed a shut off valve on the dump mast exit so that I can dump half a full gray water tank into the usually mostly empty black tank.

The procedure I use to prevent black from leaving the BW tank:

1) Close the mast shutoff - IMPORTANT
2) Open the gray tank valve - (this will fill the dump manifold)
3) Open the BW tank dump valve - (water should only flow from the GW to BW)
4) Only transfer about 1/4 of the GW volume (depends on BW level) to prevent overfilling the BW which will defeat the purpose of doing this.
5) Close BW valve FIRST
6) Close GW valve and REMEMBER the manifold is full of GW.
7) At Dump Station, HOOK UP HOSE FIRST before opening mast shutoff.
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Old 09-09-2015, 08:34 AM   #7
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Kinda doesn't make sense to do any of that when you have a black tank flush. And if you don't, then just fill the BT with water from toilet after dumping.
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Old 09-09-2015, 08:46 AM   #8
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Quote:
Originally Posted by Rugged Brown View Post
Kinda doesn't make sense to do any of that when you have a black tank flush. And if you don't, then just fill the BT with water from toilet after dumping.
Terry, I think you missed the OP's question (or I did....)
No black tank flush when boondocking.
No dump station handy or you can't move till the event is over (NASCAR).
Gray full and Black mostly empty.
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Old 09-09-2015, 08:49 AM   #9
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Hmmm; looks like it was me.

With water pressure (and no end valve) what he was talking about is not good.
The manifold would be FULL. How do you hook up the hose?
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Old 09-09-2015, 09:04 AM   #10
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Quote:
Originally Posted by Herk7769 View Post
Hmmm; looks like it was me.

With water pressure (and no end valve) what he was talking about is not good.
The manifold would be FULL. How do you hook up the hose?

Experienced a messy conclusion to that very scenario myself. That is why I always leave my transparent elbow on the end of the cleanout.
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Old 09-09-2015, 02:23 PM   #11
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I don't know if this really adds anything here, but if you have an outdoor shower/connection on your RV and water left in your fresh tank(s), I've used that while boondocking to flush the black tanks. Either with the black tank flush input or you could use the ol' garden hose with the tank flush wand through the window and into the toilet trick. And if I'm out of water in the fresh tank but I have access to a water source, I can always suck it up through the anti-freeze/winterizing inlet from a jug or bucket.
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Old 09-09-2015, 02:35 PM   #12
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This is what I have always done to rinse out the BW tank from the Gray tank water.

Empty BW tank. Grab the drain hose and lift it up and higher than the BW tank. With the hose high, reach in and pull the Gray tank flush handle. the Gray water, with soap from sink dish water will flow into the BW tank. Allow 1/4 of the GW to flow into the BW tank. Close GW tank valve and drop the drain hose to allow the BW tank to 'flush out'. Repeat twice more and on the last time leave the GW valve open when lowering the hose to allow all of the water from both tanks to flow out.
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Old 09-09-2015, 02:56 PM   #13
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Sounds messy to me. Before black flush systems showed up I use to emty black then fill with 5 gals water then go to back of camper and start pushing back and forth to josh the water around then dump again. Worked for a lot of years and never had stuck gauges either. Later RJD
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Old 09-09-2015, 05:45 PM   #14
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I was just wondering if it would work. I have have 2 gray water tanks so I I thought if you dump the bw then open the 2 gw valves it would put a pretty good gush into the bw tank loosening stuff up. I installed a tornado flush but I was just kinda thinking out loud.
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Old 09-09-2015, 05:55 PM   #15
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Using the proper amount of water, you will not have anything to 'loosenup'
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Old 09-09-2015, 05:57 PM   #16
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Agreed.
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Old 09-09-2015, 06:06 PM   #17
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I don't know about anyone else, however if you have potable water left just before you dump, fill (almost full) your toilet black water tank using your toilet (or pour buckets of water down toilet if necessary) when you open your black water valve at the dump station, that massive slug of water will carry everything out without problem! After the black valve is closed add a couple of gallons of water into the toilet tank, leave till next outing! Been doing it this way for 25+ years never had a toilet problem!
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Old 09-09-2015, 07:47 PM   #18
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The end of manifold dump valve will solve all of this and save you from "wet shoes" in the event of a tank valve failure.

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