Newyooper
Michigans U.P.
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I'm new to RVing and have a ton of questions. From what I've been seeing in videos on dumping your black tank, they reccomend filling the black tank after dumping to help flush out more debris. Why couldn't the gray water tank be dumped into the black water tank to flush it out after the initial dumping?
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LOON17
Illinois
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Joined: 10/31/2006
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It's just not plumbed that way . Lots of new rv have a built in black tank flusher. I use one that attaches at the bottom of the discharge and back flushes works good.
Tom & Karol
2008 Jayco 30.5 RLS
20 K B&W
2011 F-250 Diesel
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Artum Snowbird
Campbell River, B.C., Canada
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Mainly because if it can go one way, it can also go the other. The last thing you want is to clog that grey tank drain with some nasty black stuff.
If you are using it during a trip, just a dump is required, not a flush. Some flush at the end of a long trip, others at the end of the season.
Mike and Carole
2007 Snowbird 9'6" Super Slide
2005 16.6 Double Eagle
2000 F350 7.3 SC 4X4
previously 8'10" Snowbird Camper
2006 Triple E Regency 27 foot SXL SOLD!
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pianotuna
Regina, SK, Canada
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Hi Newyooper,
Welcome to RV net.
Some folks do do that. It requires a tight fitting cap for the sewer connection. You really don't want it to leak. Once both valves are closed you will need a bucket to catch the liquid left over. Nasty!
Another valve can be added instead of using the tight fitting cap--but unless you can do the work yourself it will cost you $$
Adding a flush kit may be a better idea and probably would be the same $$.
I usually dump after I've trundled down the road a while--that tends to "break up" any large debris. I do have a flush kit on the black tank--but not on the grey water. I wish the makers had spend the extra money to add one on the grey.
If I know the RV will be in storage for a while, I'll dump about an hour before I arrive home, add water to both tanks--and then dump again just before putting the unit into the storage yard.
Newyooper wrote:I'm new to RVing and have a ton of questions. From what I've been seeing in videos on dumping your black tank, they reccomend filling the black tank after dumping to help flush out more debris. Why couldn't the gray water tank be dumped into the black water tank to flush it out after the initial dumping?
Regards, Don
Kustom Koach Class C 28'5" 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, 2500 MSW watt inverter.
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laknox
Arizona
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Joined: 01/06/2008
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Newyooper wrote:I'm new to RVing and have a ton of questions. From what I've been seeing in videos on dumping your black tank, they reccomend filling the black tank after dumping to help flush out more debris. Why couldn't the gray water tank be dumped into the black water tank to flush it out after the initial dumping?
The on-board black tank flush systems are to help break up clumps as well as rinsing. My usual routine is to hook the hose up to my San-T-Flush, turn the water on for a minute (if not full), then pull the dump valve, leaving the flush water running the whole time. When it gets mostly empty, I close the valve and let the flush run for about 5 minutes, then dump it again, also leaving the flush water running. When it empties this time, I shut the flush off, let the remaining water drain out, then close the valve. I'll then run the flush water for about 30 seconds to put some water back into the tank. This is the biggest issue with black tanks, letting it dry out, which causes any remaining solids to dry out, making it very difficult to remove later on. I see absolutely no reason to have a flush system on the grey water tank(s). You should have almost no solids going into the grey system, barring small amounts of food and some hair. Again, you don't want to let the grey tank dry out and you should run lots of water through it whenever you can.
Lyle
2002 GMC Sierra 2500 HD Duramax Crew Cab 4x4
Banks Bullet Tuner and Monster Exhaust
B&W Turnover Ball with 5th Wheel Companion
2004 Komfort 25FSG Fifth Wheel
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Old-Biscuit
Across the USA
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Joined: 06/20/2009
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Buy a couple of slip fit glue waste valve flanges
Buy a waste valve
Cut drain line into on horizontal run close to end of drain pipe.
Bolt up flanges to valve and then using ABS glue, glue the valve flange assembly into line.
Close the new valve after dumping black tank and then open grey tank dump valve. Grey water will back flow into black tank. Close grey..open black repeat until no grey left.
New valve is also nice to have in case black or grey dump valves mal-function, leak thru or get opened by accident with end cap still on line...no surprises when removing end cap.
If you don't want to install a new valve in line.....get a twist on valve and attach to end of drain line.
After dumping black tank..always add couple gallons of water back into tank so tank bottom stays wet and tank is ready to use next trip.
Helps keep 'stuff' from sticking to tank bottom, drying out, building up.
I've installed an extra valve on last two rigs.....5 yrs. ago on current FW. Options..I like options.
2007 RAM 3500 QC LB SRW 5.9L CTD 48re 4:10 4K in bed 'quiet genny'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
Hit the Road Free & Clear April '07
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John Bridge
Houston
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I've installed the extra gate valve but only for leveling out the two gray tanks when we're dry camping. I would never co-mingle black and gray water. Never. 
Semi-"retarred" in 2006. :-) 2008 Newmar Cypress 5th wheel, 2008 Dodge diesel dually to pull it with.
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bpounds
Whittier CA
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If you do it correctly, the black won't co-mingle with the gray. Simply dump the black first, then open the gray valve and let it flow into the black. It won't be flowing back and forth. The gray will flow to black until the level equalizes, and then flow stops. Of course the end point valve is needed as mentioned by others.
I don't see any real need to do this, but it can be done and some folks do it.
2006 F250 Diesel
2011 Keystone Cougar 278RKSWE Fiver
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JohnBoyToo
DFW, Tx
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Yech !!! and dangerous too IMHO
Just do the dump in the correct order Black to grey to etc... dirtiest to cleanest and it works out...
Put on your impervious gloves FIRST.
1) dump black when close to full
2) sani flush if you have it
3) CLOSE black and dump grey tank
4) rinse EVERYTHING well and store in sealed tub. i use orange for my black stuff and have a black coiled hose for rinsing so good and bad never mix !
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Old-Biscuit
Across the USA
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Joined: 06/20/2009
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'Grey into black..black into grey'......yuk
Why yuk? Wasn't that many years ago RV's only had one (1) waste holding tank....everything went into it just like the drain system in a S&B. Same system, same drain line, all drains tied together.
Later on separate waste tanks came about.....ending up being designated grey or black and yet some bathroom sinks still drain into black tanks.
Grey tanks can be just as odorous/dirty as black tanks.
Many times folks fill up grey tank(s) faster than black tanks......equalizing them can extend capacity, adds more liquid to black tank which can be beneficial and is not going to cause any problems with either tank.
Only need to drain/flush/rinse......they are holding tanks and function exactly the same. No danger in co-mingling contents.
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