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Old 02-03-2017, 11:46 PM   #21
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Airstream has had a sketchy ownership history for over 50 years since the originator Wally Byam relinquished ownership. It was once owned by a food company! What has endured was the quality and design of its aluminum trailer shell. The interiors really were never much better than anyone else's. You can get Airstream trailers today (or last I looked) with plastic laminate counters. When it comes to their Class Bs they are middle of the road in quality but have taken the promotional effort in engaging a professional architectural designer to spiff up their interior appearance. That's a step others hadn't taken.

The reputation is in its trailer history and the timeless aluminum shell.
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Old 02-04-2017, 01:59 AM   #22
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The 2005 Interstate had first-rate appliances and fixtures for its day; it had an excellent floorpan; the folding bed/sofas were nice; it was attractive; the single gray/black tank was far superior than the stupidity of separate gray and black tanks....
I've often wondered about the merits of separate black and grey water tanks since they both generally end up dumping into a common disposal site. I notice that Avion has broken away from this convention with their Azur B that uses a single tank for both. I see that some builders are providing a fresh water flush provision to ensure that the dump hose is cleaned after the discharge which you would definitely want in a single tank system.

Perhaps the best of both worlds would be to have a setup with valving that would permit the system to operate either way - separate or combined.
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Old 02-04-2017, 02:41 AM   #23
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I've often wondered about the merits of separate black and grey water tanks since they both generally end up dumping into a common disposal site. I notice that Avion has broken away from this convention with their Azur B that uses a single tank for both. I see that some builders are providing a fresh water flush provision to ensure that the dump hose is cleaned after the discharge which you would definitely want in a single tank system.

Perhaps the best of both worlds would be to have a setup with valving that would permit the system to operate either way - separate or combined.
We have discussed this before, and several people who have never experienced a single tank system have argued vehemently that separate tanks are essential. As far as I know, I am the only member of this list who has owned both systems. I can attest without reservation that there are no advantages to separate tanks--NONE. A single tank is superior in every way. Less cost, less complexity, greater capacity for a given volume, better flushing due to greater fluid volume, simpler and faster operation, and more flexibility in using the available capacity. The solids quickly settle to the bottom of the tank, so the sequence of flushing is more or less the same. With a sealed macerator hose it doesn't matter anyway.

People claim that you can fit larger tanks if they are separate, arguing that the gray tank can conform to irregular shapes. This is just not true. The irregularities are almost always at the TOP of the tank, with bottoms flat. This works just fine with a combined tank. Obviously, one big tank has a larger capacity than two small tanks in a given space. Even if you had a space that required two tanks, you could easily connect them together to make one effective combined tank.

I have been advocating this for years, and by now I believe I have heard every argument. For reasons I don't understand, people find this simple innovation very hard to accept. But I have NEVER heard a valid rational argument favoring separate tanks. The tradition got started back when it was considered OK to dump gray water on the ground. But most people now agree that this is no longer reasonable (and it is often illegal). As far as I can see, the tradition is now just that--a tradition. The practice survives out of sheer inertia.
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Old 02-04-2017, 04:56 AM   #24
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A single large tank will require internal baffles; you don't want to do that with solid wastes.
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Old 02-04-2017, 05:46 AM   #25
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A single large tank will require internal baffles; you don't want to do that with solid wastes.
Why would enlarging a 21 gallon grey tank to 31 gallons produce a volume that would require baffles?

I don't think there is any shortage of RVs with 30 gallon black water capacity that aren't fitted with baffles.

Further, if the macerator was located at the toilet rather than the pipe-end, the grey+black tank hydraulics wouldn't be any more an issue than it is for even larger typically unbaffled fresh water tanks.
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Old 02-04-2017, 01:56 PM   #26
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The way I see it there is a simple reason for a separate black and grey tank. If you have a 3" gravity slinky type hose or a macerator 1-1/2" hose, first dump your black tank then check all your joint fittings. Generally you'll have a crud buildup and hung up TP that you would then have to thoroughly clean with a water hose. That is what you'll get if you have the single tank. Then run your grey water through which is mostly soapy water and typically twice the volume. That second grey water dump will do most of your hose and fitting rinsing leaving any necessary water cleanup as almost but not quite a cursory step I think more for odor control. The benefit is less fresh water use. I had the single tank in my Airstream trailer, a two tank slinky dump and two tank macerator dump. I've observed the difference.

There is also a design function involved especially in Class Bs that are low to the ground. Most black tanks sit higher to get a more positive gravity discharge which is why a toilet looks as if it is on a pedestal in your bathroom. Typically such a design is why most tanks are in the 9 to 11 gallon range which is pretty much a physical limit. They seem easier to maintain since you can see much of your black tank looking down the toilet discharge with a flashlight to see the condition of it. Then you have flexibility in locating your grey tank which is generally going to be about twice the size of your black tank in most Bs. Tank locations in a Class B have more restrictive physical limits and, of course, weight and distribution limits.

Another aspect is odor control. Traps dry out or slosh out frequently and you can detect the foul smell from a grey tank. As foul as it is it is not nearly as foul if it were combined with the nose searing blank tank contents. The black tank has one source of odor and that is the toilet trap that can easily be maintained.

Older RVs did have single tanks. The two-tank system evolved over time and I doubt converters will regress. Campground infrastructure has adapted to it which has pretty much negated the need for the next solutions of cassettes and so-called composting.

Cassette toilets and composting toilets have more severe physical limits causing more frequent dumping and unsanitary direct handling, and then you still have your second and totally separate step with grey water disposal which takes you to the same places to dump as conventional RV users. This concept in a B is hard for me to fathom. Yeah, I understand the idea of going off-road remote and flexible choices of dumping and winter use for compost toilets but in reality those are probably low percentage times of overall use and even that romantic private site by a lake is known to others and I doubt they would appreciate parking next to a grey water dump on the ground cesspool or find the dump pile in the bushes. Clearly in a confined close campground such practices couldn't be tolerated. You do know that if such practices were the majority of RVs there would be abuses that eventually could not be tolerated similar to the fact I've never met a person that doesn't dispose of cigarette butts properly or not clean up after their dogs. Yeah, sure.
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Old 02-04-2017, 02:07 PM   #27
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What the architect said +1


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Old 02-04-2017, 02:22 PM   #28
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I agree that separate tanks are a good idea with a slinky drain system. With a properly-designed macerator, the drain hose is part of the sealed system and needs no cleaning. Plus, as I said, in practice the gray water (being less dense) tends to drain last anyway. I know this from actual observation over a long period of time.

To my understanding, the reason older RVs had a single tank was because it was exclusively a black tank. Gray water used to drain onto the ground. I'm sure there are exceptions (My 2005 Interstate being one), but if there was ever a period where combined tanks were common, I am unaware of it. So, the change would (hopefully "will") be progress, not regress. I seriously miss that aspect of my Interstate.

I agree with the part about composting toilets.
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Old 02-04-2017, 04:34 PM   #29
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Dean always makes a great presentation of P/W. I notice the gravity feed sewage pipe - and have looked at other models and prior years, do they offer a macerator..or is it a possible retrofit.
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Old 02-05-2017, 04:41 AM   #30
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When you've overfilled your waste tank (and it happens to everyone at least once) and raw sewage backs up into your sinks and shower, then you'll understand perfectly why separate tanks are essential.
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