Black and Grey Tanks

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JamesOne

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Why do RVs have a black and a grey tank? Most boats have just one holding tank. Is there some government regulation requiring the separate tanks in an RV?
 

Steve CDN

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In some situations the grey tank can be easily dumped or emptied, whereas the black tank cannot.  By isolating black and grey, the RVer has flexibility in managing waste.

Most boats have just one holding tank

Is that why some boaters just empty all their waste into the waterways?
 

Ned

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There are some RV models that have a single holding tank.  The ones I've seen are mostly high end motorhomes.  A single tank does simplify the waste management problem, especially when boondocking.
 

Karl

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James,

I don't know if there is any regulation in place, but there are a few reasons to keep them separate. If you notice your gray water tank is getting nearly full, you can cut back on things like long showers and switch to washcloth or sponge baths, and cook things other than 10 gallons of pasta at a time until it's convenient to dump. You don't have that option with the black tank; GIGO. The gray water is also used to flush the hose after dumping the black tank. More sanitary that way. In theory (if not in practice), you could use the gray water to water outdoor flowers.  However, gray water tends to be as stinky as the other stuff.
 

Ned

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I doubt there are any legal ramifications, as the tanks now dump into the same systems anyway.  Your advantage is actually an advantage for a single tank, as I mentioned, no waste management other than to not fill the single, larger, tank.  No dumping dishwater down the toilet because the gray tank is full.  As for flushing the hose, I flush the holding tank with fresh water after dumping and then flush the hose out too.  I would much prefer a single 100 gallon holding tank over my 40 gallon black and 60 gallon gray tanks.
 

Tom

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On a boat, gray water goes directly overboard, or pretty close to directly (not into a holding tank), so only a black waste tank is used. It is illegal to dump gray waste from your RV onto a street or even into a rain water drain; It has to go into a sewer.

For clarification, there are some waterways that have restrictions on the overboard discharge of gray water, but that's a more complex answer.
 

Tom

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Steve said:
Is that why some boaters just empty all their waste into the waterways?

Steve, hopefully, nobody is emptying the untreated contents of their black waste tank into waterways. It's illegal anywhere in inland waterways within the U.S. and anywhere out to 3 miles offshore. Some boats have a black waste treatment facility on board and the output of that system can be pumped overboard in most, but certainly not all, waterways; There are some very clear "no discharge" zones.

FWIW most (but not all) power boats with on-board heads have a dual discharge system - either pump overboard or a connection to an onshore pumpout facility. In these cases, unless the contents of the tank have been treated, the U.S. Coast Guard regulations require that the Y-valve between the two systems is physically locked in the "no overboard discharge" position. They will check the position of the valve when they board a vessel.

In addition to Federal regulations and enforcement, most states also have their own regulations and enforcement that, for the most part, supplement (not replace) Federal regulations.

What are the laws on Canadian waterways, how are they established and who enforces them?

Edit: Looks like Canada has similar laws for sewage control on recreational vessels. See the Transport Canada web site.
 

JamesOne

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In some situations the grey tank can be easily dumped or emptied, whereas the black tank cannot.

Can someone tell me a situation where a grey tank can be legally emptied and the black tank cannot?
 

Jeff

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JamesOne said:
Can someone tell me a situation where a grey tank can be legally emptied and the black tank cannot?

James:

There are still parts of the US that allow settling pits for grey water at some campgrounds. These are for dishwater only.
 

Carl L

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JamesOne said:
Why do RVs have a black and a grey tank? Most boats have just one holding tank. Is there some government regulation requiring the separate tanks in an RV?

I do not know why the idea originated but I can tell you why it is a good idea.  When hooked up to the sewers at an RV camp, one leaves the black tank shut but the grey tank open.  The black tank contains solids.  By keeping the tank shut the solids get attacked and emulsified by the bacteria in the tank.  Then when the tank is a bit over 2/3s full, dumping it causes the remaining solids to be swept out in the current.  If the black tank were left open, septic action would not take place and the solids would accumulate as crud, leaving one with a major cleaning problem.  Greywater tanks have no solids and can be left open full time.  This makes dishwashing and showers simpler propositions -- no worries about tank overflow.

Of course people in huge motorhomes with 100 gallon tanks do not have to worry like the little people.  ;D

 

Ron

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Jeff Cousins said:
James:

There are still parts of the US that allow settling pits for grey water at some campgrounds. These are for dishwater only.

Just be sure the dumping of grey water in these pits is an approved practice before you try it. ?Fines can be pretty stiff if not approved.
 

Ned

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If we had just one tank, I would let it fill to about 3/4 full and then dump it.  I would never leave the drain open.  100 gallons would last us a week or so.

Another advantage of a single tank is it would typically be the same size or larger than the fresh water tankage, so when boondocking, there is no concern about filling up the holding tank.  With separate tanks it's possible to fill the gray tank with plenty of room in the black tank.
 

buckle823

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I think there should be a bypass system to divert overflow from the grey water tank to the black. Our grey water fills up super fast, and when I go to the dump site, my black water is still like at 1/4. Short of pouring dishwater from a sink liner down the toilet, there is no easy way to take advantage of the extra space in the black water tank. Does anyone know if there is a bypass system available?
 

Tom

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buckle823 said:
Short of pouring dishwater from a sink liner down the toilet, there is no easy way to take advantage of the extra space in the black water tank.

That's one of the techniques used by many folks here when boondocking for an extended time. (IIRC Fred Thomas is the one I heard it from first). Here's a boondocking primer compiled from various sources that includes a few other tips.

Sorry, I'm not aware of a bypass system, but maybe someone else does.
 

buckle823

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Check this system out:

http://www.ccis.com/home/mnemeth/grwater.htm

I think I will rig this up for sure.
 

Ned

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That's certainly one solution, but only if you have access to the requisite plumbing.  In our case, there is no way I could plumb in to the black water plumbing as there isn't any.  The toilet drains directly into the holding tank and there is no access to the top of the tank.
 

buckle823

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Good point Ned. I think I will get a small electric pump and just keep the stopper in the tub during showers. Pump the bath into the toilet.
 

Ned

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If you take Navy showers, you can shower in <2 gal. of water.  We have gone for up to 10 days on our 60 gal. gray water tank when boondocking.  Most people waste more water than they use and some simple conservation practices will stretch your water supply and holding tankage a long way.
 

ArdraF

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some simple conservation practices will stretch your water supply and holding tankage a long way

There's that wonderful word conservation.  After having our water rationed in California two different times and both times for several years, we learned a lot of ways to conserve that precious resource water.  One of our best ways is a simple little device we put on the bathroom faucet that prevents water from flowing except when you push out of the way the little rod that hangs down from the faucet.  Washing our hands and brushing our teeth while having the water faucet on is one of our biggest water wasters.  We bought these devices at Camping World for about $12.  They're called Water Saver and are easy to install - just take off the old faucet end and screw in the WaterSaver.  In addition, having an on-off feature on your shower head allows you to turn the water off when you're soaping up without losing your hot water adjustment like you do if you turn off the shower completely.  You probably have a double kitchen sink.  We have a designated "clean" side that we keep covered most of the time.  When washing dishes, I do not allow water to run.  I fill both sinks then wash in one side and rinse in the clean side.  We've used these three simple measures for many years in all our RVs and they save a huge amount of water.  Needless to say, we do not use the washer-dryer when boondocking because we don't want to wantonly use water or fill the gray tank.  With judicious water usage we can go for 7-10 days before dumping.  Oh yes, when boondocking for any length of time like at rallies we use paper plates so I don't have to wash dishes as often.

ArdraF

 

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