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Old 07-03-2016, 06:30 PM   #1
mre
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Black and Gray Water Tanks

DW ask me a question today that I never really thought about (well maybe a little). Why are RVs made with both a black and gray water tank? I have heard from a few people who periodically dry camp, that the install a valve over the drain opening. They will open the them if the gray water tank become full. Anybody know?
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Old 07-03-2016, 06:40 PM   #2
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Some people have very unhealthy practices with their water management. That said some places gray water can be dumped places black cannot.
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Old 07-03-2016, 08:52 PM   #3
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Great question. I would much prefer one large tank with a pressure tank clean system.

I've only run into one state forest where dumping gray water was OK. But the thoughts of food particles from washing dishes and big bears nearby kind of made me to not dump it!
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Old 07-04-2016, 12:22 AM   #4
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Great question. I would much prefer one large tank with a pressure tank clean system.

I've only run into one state forest where dumping gray water was OK. But the thoughts of food particles from washing dishes and big bears nearby kind of made me to not dump it!
In 25 years I have been RV camping, I have only run into one campground that allows dumping grey water in a hole in the ground which looked to be filled with gravel. I have seen a few other places in remote areas that turned a blind eye.
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Old 07-04-2016, 01:19 AM   #5
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For MANY years trailers (RVs) only came with ONE waste holding tank.

Then more and more amenities were added necessitating larger capacity waste tank...so multiple tanks were installed due to space constraints
(1974 separate tanks started being used)

Black and grey then galley

I have 3 waste 'holding' tanks that all drain thru a common drain header.
So I have an extra valve on end of drain header (something I do to all my RVs/trailers)
1) little extra protection should a tank drain valve leak
2) can increase waste holding capacity as needed
Galley to grey (28 to 50====78)
Grey to black (50 to 50====100)
Galley/grey/black (28-50-50=== 128)

Some RV mfgs. even plumb bathroom sinks/showers to black tanks now

It's ALL waste water!
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Old 07-04-2016, 07:37 AM   #6
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Some RVs have sink water and toilet draining to the same tank. The main advantage of separate tanks that I can see is if you are hooked up to a sewer site you can let your shower water drain and not accumulate. You need to hold your black water until ready to dump to prevent a mound of waste plugging up your drain system by having a enough water mixed in with to waste to make it flow. If you used the toilet with the black drain valve open all the time the water would flow out faster than the waste and it would leave a mound of waste behind in your tank. Some people have a phobia about the black and grey water tanks being hooked together, but they must not realize that in any house all the waste, no matter the source, goes out the same sewer pipe. It's the "p" traps in your house and in your motorhome that keep the smell from coming up through the drains.
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Old 07-04-2016, 08:21 AM   #7
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Some RVs have sink water and toilet draining to the same tank. The main advantage of separate tanks that I can see is if you are hooked up to a sewer site you can let your shower water drain and not accumulate. You need to hold your black water until ready to dump to prevent a mound of waste plugging up your drain system by having a enough water mixed in with to waste to make it flow. If you used the toilet with the black drain valve open all the time the water would flow out faster than the waste and it would leave a mound of waste behind in your tank. Some people have a phobia about the black and grey water tanks being hooked together, but they must not realize that in any house all the waste, no matter the source, goes out the same sewer pipe. It's the "p" traps in your house and in your motorhome that keep the smell from coming up through the drains.

In your home there is a pitch to your drain pipes, you use at least 1 gallon of water to flush and the pipes are not flexible with a accordion sides. How many time have you hooked up your sewer hose to the campground drain and made sure you had minimum required pitch on that expandable hose?

Use plenty of water when you flush, if possible do not dump the black tank until it is 75% full add extra water to the black tank before you dump and have a full grey tank to flush it all down. You reduce the problems and be a happy camper.
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Old 07-04-2016, 11:17 AM   #8
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I think they are separate as a health issue. Ever overfill the grey tank? On the rare I ocassion that has happened I would rather be standing in the shower in grey water than raw sewage, nor would I like it backing up into any other drains.
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Old 07-04-2016, 12:23 PM   #9
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I think they are separate as a health issue. Ever overfill the grey tank? On the rare I ocassion that has happened I would rather be standing in the shower in grey water than raw sewage, nor would I like it backing up into any other drains.
Grey waste water can be as nasty as black.....

Rotten/decaying food debris, greases, scum, body oils, skin cells, urine (just like swimming pools folks will pee in shower), fecal (from washing you butt), bacteria from mouth

So don't fool yourself into thinking grey is just sorta dirty water.......
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Old 07-04-2016, 02:32 PM   #10
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I think they are separate as a health issue. Ever overfill the grey tank? On the rare I ocassion that has happened I would rather be standing in the shower in grey water than raw sewage, nor would I like it backing up into any other drains.
While grey water tanks can be nasty, they are not as bad as black tanks. If your black tank were connected to the grey tank, or if you only had one tank. You would not be able to keep the grey tank valve open. It would limit showers especially if you have g-kids with you. You would constantly be opening and closing the grey tank. What about using a washing machine you'd have to keep the valve open for that. Too many reasons to have separate tanks.
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Old 07-04-2016, 04:01 PM   #11
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While grey water tanks can be nasty, they are not as bad as black tanks. If your black tank were connected to the grey tank, or if you only had one tank. You would not be able to keep the grey tank valve open. It would limit showers especially if you have g-kids with you. You would constantly be opening and closing the grey tank. What about using a washing machine you'd have to keep the valve open for that. Too many reasons to have separate tanks.

I disagree, grey water tanks are quite often not treated and when all the food bits go down there the smell can get BAD, many mistake that for a black tank problem. You should not keep the grey tank valve open, an RV does not have the pitch to the pipes your home has, you can not guarantee a clean drain into the campground sewer system so you need to keep a volume of water that is released all at once by the flush valve. Yes, it can mean you dump the grey every couple of days, but it the best way to be sure all goes down the drain.
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Old 07-05-2016, 12:04 AM   #12
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so my first class C years ago had one tank.. it was never large enough... my current unit has 3... 2 gray 1 black.. each has its own drain valve and there is a common drain valve where the sewer hose connects to the unit... sometimes when parked on private property with the permission of the owner I might drain the 1 gray tank that supports the shower... for us its the tank that fills first as we both enjoy a nice hot daily shower...

I just think its a manufacturing convenience... unless they are trying to prevent sewer gas, methane from maybe getting through a dry trap on a shower or sink from running down the highway.... and putting that methane gas in the coach..
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Old 07-05-2016, 05:49 AM   #13
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I disagree, grey water tanks are quite often not treated and when all the food bits go down there the smell can get BAD, many mistake that for a black tank problem. You should not keep the grey tank valve open, an RV does not have the pitch to the pipes your home has, you can not guarantee a clean drain into the campground sewer system so you need to keep a volume of water that is released all at once by the flush valve. Yes, it can mean you dump the grey every couple of days, but it the best way to be sure all goes down the drain.
I agree, Grey water tanks are quite nasty and most RV'ers don't treat the Grey tank.
However while all of you out there are so worried about these tanks, they don't bother me. I don't use gloves because I'm use to having to dump sanitary onboard the submarines. Just think thousands of gallons thru a pressurized 4" hose. And if you screw up the valve lineup, what a mess
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