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Old 10-28-2003, 10:34 PM   #21
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59toaster:

You mentioned that you were thinking of fabricating a greytank out of aluminum.

I am having All-Rite (www.all-rite.com) custom make a plastic grey tank, with all the fittings right now. They'll quote you a price over the phone. Mine is 4"x54"x22", and will fit between two cross-members, which are 24" on center. The tank will be wrapped with foil-bubble insulation, and sit on 1" steel angle brackets. It will drain to a T, where one pipe goes through a Drainmaster electric dump valve, then a check valve and into the black tank, and the other pipe goes to the drain outlet.

Attached is an image showing how the tanks fit in the frame. Mentioned elsewhere on this thread was talk of a macerator. My black tank is connected to a Drainmaster dump valve, which is connected to a Jabsco macerator pump. The Drainmaster fits inside the galvanized metal box, and the macerator could have been mounted either half-way into the box, or fully inside the bumper box. Since I'm still building this, it has not been tested in the real-world.

Christopher
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Old 10-28-2003, 10:48 PM   #22
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Greytank

Really great work, Chris.
Aren't you concerned about the macerator pump sucking air once the tank is half empty?
I was going to build a small sump with three inch elbow angled down 45 to a low heel Tee, with the pump at the top and a 2" pick-up to the bottom of the capped tee. (I can send you a .dwg if you're interested, it's a little hard to describe verbally)
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Old 10-29-2003, 02:00 AM   #23
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Toaster,

Thanks for the link, most interesting, I was on the road for 2 months & missed all these posts.

Mark,

got all the pics & answers I wanted in the great september thread.

I'm impressed with the skill you guys have!
I can't even consider removing a few rivets to take a peek at the frame! although I'd love to know if it's still solid.

Hart
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Old 10-29-2003, 09:39 AM   #24
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Mark,

The macerator pump makes a different sound when it gets to air, rather than liquid. There are no p-traps in a black tank, so the air that gets sucked out of a black tank is replaced via the tank's vent through the roof. Also, the switch for the macerator is not the type that you turn "on" and walk away, it requires you to hold it "on", because it only takes about 90 seconds to empty a full tank the size of mine.

The particular macerator pump (Jabsco 18590-1010) has run-dry protection, so it won't burn out right away when there isn't any more liquid to pump. Be sure your sump pump has this protection. Also, the macerator pump clamps right onto the existing 3" sewer outlet, so it is very easy to install, and doesn't stick below the belly pan, like I'm assuming a sump pump hanging off a 45 elbow would. In my particular case, the macerator runs horizontally right out from the tank, and is bolted to the frame under the bumper storage area. The 25' long, 1" diameter hose is stored in there as well.

Christopher
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Old 10-29-2003, 10:02 AM   #25
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Chris:

Man you tickle me to death with all the hightech graphics and the upgrades your doing to your coach.



Anyone:

Let me ask this. Other then making the plumbing that Mark addressed in his plans being a little more complicated why is there not the option to dump the gray into the black from the factory?

I understand that there are instances where they may need to be dumped indipendently but if you could dump the gray into the black after draining the black that would let you get a little rince action going.

My black is above the floor so this would never be possible but on coaches with both tanks below the floor you could easily dump a fair amount of a full gray into a empty black without pumps.
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Old 10-29-2003, 10:16 AM   #26
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This is a good question and leads to the reason that Airstream is going to a one tank system. It is also less complicatted and I am sure saves money and time on the build. A good flush thru the black makes sense.

The only negatives I can think of are if the trailer is not level then you may not get all of the grey out, or you may have a reverse flow. Also if the black tank has a problem, leaky valve, stuck valve, or blockage you are really stuck. If you are on a trip, and doing the trip with just overnights you may not need to dump the black for a week, but the gray could need it daily.
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Old 10-29-2003, 10:38 AM   #27
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gerbermania,

I see your existing black tank is 7x48x22. This is 7,392 cu. inches, which equates to 32 gallons by my math. But you have it as just 17 gallons. Is the "cutout" area by the drain accounting for the difference, or am I getting something wrong?

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Old 10-29-2003, 01:32 PM   #28
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Grey tank mod.

Christopher:
Yeah, I understand about the different sound and the run dry protection, but the problem I see I that as soon as the pump starts seeing 'air' at the suction side, you lose pumping efficiency and start pumping foam. If it were a centrifugal pump, you'd lose prime as well, but Jabsco are flex impeller pump so that's not a problem.
Yeah, having a small sump does create some hangdown problems, but i think I have enough space and am close enough to the axle that wont be a problem for me.
How do you post those great renderings? File type?
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Old 10-31-2003, 05:54 PM   #29
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59toaster:
Thanks for the compliment. I find that graphics like these are the best way for me to work challenges out. I like solving challenges before they become issues. As far as dumping the grey into the black, I have added a dump valve in my system which does just that, see the attached image. In the pipe going from the grey to the black tank, there is a a swing check valve to prevent backflushing of black into grey, then a "T" for the greywater bypass, then a dumpvalve. The dumpvalve can only be used, however, if the black tank is 1/2 full or less, otherwise the tanks level each other out. Best case scenario, I dump excess greywater into the black tank, effectively increasing the size of the grey tank. If I were the lead designer at AIRSTREAM, I would still design at least two tanks, black and grey, I would not combine them. It is a waste of water, to use potable water to flush the black tank. By using the greywater from other larger tanks after dumping the black tank, potable water is conserved. That being said, I would *LOVE* a 50 gallon grey tank, and a 50 gallon freshwater. As it is, I have a 17 gallon black, 17 gallon grey that I added, and a 25 gallon freshwater. The grey tank cost me $400 from www.all-rite.com, otherwise I'd add an additional one under the floor for freshwater. I've squandered enough of my son's college fund.

rluhr:
Too funny, who's chekcing your math? The attached image should explain a bit more. The tank varies in depth from 7" to 4". Those were exterior dimensions, and the tank is roto-molded, so the sidewalls are approximately 3/8" thick. If you like math, cool, I prefer the tank calculator at: http://www.watertanks.com/calc.asp

markdoane:
Good points. Like you said, the Jabsco is self-priming, so I expect it to act more like a vacuum when it starts to create foam. It is mounted horizontally straight out from the tank outlet, which is the lowest point of the tank, so it should suck out most everything. I built a connection to flush my greywater through the black tank, once the black is emptied. That should clean it up pretty well.

As far as my renderings, I typically 3Dmodel in AutoCAD and Rhino, and render images with Penguin and AccuRender. I do most page layouts and presentations with PowerPoint, and edit my images in PicturePublisher. These are tools I use daily as an architectural designer.

Christopher
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Old 03-06-2006, 10:20 PM   #30
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So... a few years later.. Uwe, did the vent work?
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Old 03-06-2006, 10:36 PM   #31
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Originally Posted by ankornuta
So... a few years later.. Uwe, did the vent work?
Andrew,

Yes, it worked like a charm. Even though the sink drain connected to the side of the tank at about the middle, the tank filled up nicely after the mod was done. I had 2/3 more capacity.
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Old 03-07-2006, 10:53 AM   #32
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The people at the RV parts store (not necessarily experts, I know) told me that all the drains had to come into the top of the gray tank. That didn't seem logical to me, so long as the drain opening (i.e. sink, shower) is above the highest point of the tank. It sounds like you're not running your drains into the top, you mentioned it connects into the side of the tank. So anyhow, this hasn't posed any problems?
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Old 03-08-2006, 06:07 AM   #33
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Originally Posted by ankornuta
The people at the RV parts store (not necessarily experts, I know) told me that all the drains had to come into the top of the gray tank. That didn't seem logical to me, so long as the drain opening (i.e. sink, shower) is above the highest point of the tank. It sounds like you're not running your drains into the top, you mentioned it connects into the side of the tank. So anyhow, this hasn't posed any problems?
As long as there is a vent in the top of the tank, it will fill completely, regardless of where the inlet is.
My sink inlet was in the side of the tank, 1/3 of the way down, the shower inlet was through a T in the bottom outlet.
It was a problem before Isintslled the vent. The tank would only fill to the level of the sink inlet. After vent installation, it filled pretty much completely, to the point where it would back up in the shower pan. I did not have atnk sensor on this add-on tank, so every once in a while the tank would get too full.
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Old 03-08-2006, 07:50 PM   #34
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Ahhh... that makes sense to me. Thanks for your continued support!
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