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Old 12-06-2002, 11:48 AM   #1
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1999 25' Safari
Edina , Minnesota
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Posts: 183
Question My dumb question about holding tanks

Precisely why are there separate grey and black water holding tanks on late model trailers? Why not one big one, or a means of transferring waste from one to the other depending upon which one fills first? Are lots of people draining grey water onto the ground? Its illegal in MN and many other states.

I have never seen a situation where I could dump the effluent from either tank in anything other than an approved sanitation station, so I don't understand why there isn't a better way to optimize the capacity of waste tanks. It would seem easier to empty and flush one tank rather than two.

I either fill up the black before the grey or vice versa and would like to have a way of filling both before I have to empty one. I carry 45 gallons of fresh, but have only 23 gallons for black and with my three women and me, it can fill fast when we are boondocking.

Just curious.
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Old 12-06-2002, 12:07 PM   #2
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The black tank is only for the toilet. The grey is for shower & sink use. They are separated for sanitary puposes...if they were combined and were to overflow, say into your shower (it's usually the lowest point) you'd have a "mess" to deal with.

Our '64 does not have a grey tank. We collect that waste in a "blue belly" and dsipose of it separately...our black tank is only 10 gallons or so.

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Old 12-06-2002, 12:40 PM   #3
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Tanks fill up and when they do the lowest drain catches the overflow. This usually means tub or shower. Think about a consolidated black and grey water tank if this occurs. This also means that your trap in the drain has now been contaminated by sewage. Not a good situation.

As far as grey water on the ground, I have mixed feelings. Personally I don't think its a bad thing in the right situation. Really most grey dumping bans are a case of lumping everyone in the same group because of a few bad eggs who abused their dumping, like turning their neighbors campsite site into a swamp while they shower. Quite honestly go out to most public facilities and you will find that the tent campers dump their grey water at their sites albeit in smaller quantities.

From my experience most grey water dumpers only do it when it can be done with little impact to the site and environment. Most also do it under the cover of darkness.

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AIR #56 S/OS#15
'04 Classic 30' S.O.,'03 GMC Savana 2500
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Old 12-06-2002, 01:53 PM   #4
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A good ole holiday memory for you,

Reminds me of National Lampoon's "Christmas Vacation", when Randy Quaid was dumping his MH's sewage down the storm drain in front of Chevy's house!!

Former Airstreamer
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Old 12-06-2002, 01:59 PM   #5
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I've done it!


I've over flowed into the shower a couple of times. Fortunately I caught it before too much water came in . It amazing what kind of flush, in volume, when you drain at this level!!!


That's a classic scene and Randy does an awesome job!!!

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Old 12-06-2002, 05:36 PM   #6
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1999 25' Safari
Edina , Minnesota
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OK. You've proven that you are all more thoughtful than I. (I already knew that) And, yes, I had not thought of the overflow situation, but...why not then put backflow preventers on the grey drains, as there are only three, generally. Or, have a very large black tank and slightly smaller grey if necessary, but have the overflow from the grey go into the black, again with a backflow preventer so the black does not contaminate the grey.

We generally are in more rustic campgrounds, frequently with no sanitation stations, so I must dump in rest area or service station dump stations after we leave the CG and are on the road home. A "honey wagon" is not really an option, either.

It is not uncommon for me to refill my fresh water, however, as that is almost always available, so that is why I fill one tank or the other and would like to optimize the capacity usage.

Obviously, I had too much idle mental capacity today to come up with such a goofy question. The title forwarned you all!!
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Old 12-07-2002, 01:22 AM   #7
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Check my post in "toilet replacement"

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