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Old 04-06-2018, 12:07 PM   #1
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2016 23' Flying Cloud
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Question: Grey vs. Black water tank sizes

We have 2016FC23D. It has 39 FW Tank, 21 GW Tank and 18 BW Tank.

I wonder how these sizes were determined by Airstream designer.

As everyone knows, GW tank fills up pretty fast if you are not careful. On the other hands, it would probably take more than a week for two people to fill BW tank (as a matter of fact, we have never filled BW tank).

If I was designing a trailer, I would make GW tank bigger and BW tank smaller. It makes sense, right?
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Old 04-06-2018, 12:56 PM   #2
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My Interstate has a 26-gallon fresh tank, 26-gallon gray tank, and 17-gallon black tank. Which works out perfectly. Fill the fresh tank instead of hooking up to municipal water, and by the time the fresh tank is empty, it's time to dump the black and gray tanks. No chance of overfilling either waste tank that way.
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Old 04-06-2018, 02:34 PM   #3
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21+18 = 39

That is not reality for most folks, but it is logical from a numerical perspective. Perfect mass balance, if you will. Since the tankage is less in the CB/D than the FB, I have always suspected that the tank size was what fit as opposed to ideal for use. Guess you could call that an analysis with poor logic as it's pure suposition. The weight balance of the trailer is likely the boundary condition that AS engineering is using as prime. Pat
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Old 04-06-2018, 02:53 PM   #4
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My 75 has a 45 gallon fresh water, 12 gallon black and 10 gallon gray. This means you can dump the tanks twice and still have some fresh water in the tank. Things are much better today.
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Old 04-07-2018, 09:35 AM   #5
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Traveling solo I'm likely to fill the GW tank before the BW. I wash dishes in a plastic dish pan and dump that into the BW tank to fill it up for a good flush of the tank and a good rinse when the GW is full. I suspect the sizes were determined by average use (not withstanding available space under the floor plan; i.e. balance and weight distribution).
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Old 04-07-2018, 07:29 PM   #6
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Some newer, smaller Airstreams are routing some gray wash water to the black tank to help even things out a bit. I understand there may be one shorter Airstream model that has only one tank for both effluents.

I also have a 75 Airstream (Overlander) that has a big fresh water tank just ahead of the axles and then a small black and very small gray tank clear at the back of the trailer. I have removed the old, broken and inadequate tanks and replacing with a 27 gallon black tank and a 27 gallon grey tank. I have routed the bath sink to the black tank. The galley and shower drain to the gray tank.

Airstream literature back then talked about being able to boondock for a week with the holding tanks. Maybe so back then. The citizens of Cape Town South Africa are trying to live on 5 gallons of water per day per person. I suspect many Airstreamers use more water than this per day.

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Old 04-07-2018, 07:51 PM   #7
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Who knows how the numbers are determined??? I like the 21 + 18 = 39 math but that doesn't hold true for our trailer. According to the specifications on our trailer we have 54 fresh, 39 gray, 39 black. The math doesn't work on our trailer.

I suspect the chassis/frame layout, the weight rating of the axles, location of plumbing and appliances, etc. have quite a bit of influence on tank sizes.

Your 21 gallon gray tank is the weakest link in the equation but even that capacity should allow two people to shower every day and wash a limited amount of dishes for 3 to 4 days. We almost always use our fresh water tank and the on-board pump for our water use. We do this in our trailer as well as our van. Our Interstate van only has slightly more gray water capacity than your trailer and two of us can go 5 to 6 days without much thought on water usage. The key is to be very aware that when the water pump is running that water is coming from somewhere (the fresh water tank) and is going somewhere (the gray and black water tanks). Adults can be "trained" to use very little water - it's a bit more difficult with youngsters.
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Old 04-09-2018, 01:03 PM   #8
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If holding tank capacity is a problem. Change over to a composting toilet and use the black tank for additional waist water storage. I sure like mine and the wife likes the longer showers.
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Old 04-09-2018, 01:23 PM   #9
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We just accepted the tank size to be what it was. Our use fills the grey water in about three days. We never fill the black tank. So if we were ever to purchase another coach, we might give tankage more thought. The good news is that we like Glimmer just fine. After three days it's time to move the adventure down the road. Ain't live fun when you travel in an Airstream, Silverstreak, Avion .... Pat
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