Sunday, November 2, 2014


My husband and I were in the process of DIY-rehabbing our Airstream Interstate's gray water tank (see Part 1 and Part 2 of that process) and we were about to re-install it when this rather shocking Sprinter and B Van Forum thread titled "The Flood" revealed a design problem that is apparently known to many.  If the Interstate galley sink faucet is turned off but the control lever remains in the "wrong" off position, the water will turn back on once the glass sink cover is lowered.
To my knowledge, most Interstates are built with the recessing faucet and tempered glass cover.  Those are the ones affected by this problem.  Reportedly, the same folding faucet has been used in all Airstream Interstates produced to date with the tempered glass sink cover, regardless of model year, so you are at just as much risk if you have a new Interstate as an older model such as ours.  
What happens in this situation comes close to any RV-er's worst nightmare:  Unless the owner notices that the lowering of the glass cover has nudged the faucet lever back into the "on" position (and the owner is often unaware because the problem can develop silently, particularly if the vehicle is hooked up to shore water such that the pump is not running), the water continues to run invisibly inside the closed sink, eventually filling the gray water tank, backing up through the shower drain, and flooding the interior of the coach.  Depending on how full the gray water tank was to start with, flooding can occur in a matter of minutes of the faucet being accidentally actuated.
Trust me - given time, I would screw this up.  Even after being told about the problem, one day I would forget.  It would be late in the day, I would be very tired after hiking eight miles through the mountains, and I would accidentally flood the RV.

In my opinion, this is potentially dangerous.  The electrical system is largely mounted on the floor of the coach.  The charger/converter is just a few feet away from the wet bath.  Our coach battery is under our passenger's seat, and a bunch of electronics and wires are beneath the driver's seat.  Water and electricity do not mix, and yet apparently Airstream has done nothing about this risk across numerous Interstate model years.
Users both on- and off-forum have not yet reported achieving a solution by modifying or retrofitting the faucet itself (insert long story here involving a foreign manufacturer, inability to procure parts, lack of compatible aftermarket options, etc.).  For that reason, and because our gray water tank was already dismounted from the vehicle for unrelated repairs, my husband and I decided that we would ignore the faucet and instead mitigate this risk by installing an emergency relief port on the gray water tank.   That way, if we ever screw up our faucet lever placement (which we eventually will), the excess water will discharge harmlessly beneath the chassis rather than flooding the interior of our coach.
Like many other posts I write, we are breaking new ground here, inventing new and untested procedures, and we have no idea whether our devised solution will actually do the intended job.  See BIG FAT DISCLAIMER.  
To our knowledge, there is no plumbing device on the market today that is designed to serve the function of an RV gray water tank overflow relief port.  Furthermore, my husband's research revealed that it is important not to interfere with the venting of the gray water tank.
If you check your Owner's Manual, you will find reference to a vent line in the roof of your vehicle extending from the tank.

Beware, though, the issue of inaccurate or overly-generalized Owners Manuals.  This 2007 manual makes reference to the "black/grey" tank when in fact our 2007 has two completely separate tanks.

Diagram screengrabbed from Airstream published materials.  
The vent line is designed to release odors to the outdoors rather than to the interior of your coach (up through the drain lines), and also to equalize pressure when the tank is being dumped.  If the tank were to be penetrated by an additional unrelated structure such as a simple open relief pipe, this odor conveyance through the vent might get short-circuited.  Therefore, the relief structure had to have some sort of movable part that would remain closed for air but open in an emergency to allow the passage of faucet-driven flood waters.
This sump pump check valve is what we found to accomplish that goal - although our plan was essentially to install it backwards.  In other words, we are not trying to prevent the backflow of water - we are trying to allow the escape of water while having the flapper prevent the re-routing of air.

We bought this model because it was available locally at Home Depot - there are others on the market.  Be sure that whatever you choose is not too tall for your application.  Normally, when used on sump pumps, there is no concern about clearances, so many of them are long.  
There is the little flapper in the device.  The end you are looking into here will be the end pointing down into the gray water tank.  
This is the view from the opposite end, with me sticking my finger into it to raise the flapper enough for it to be seen through.  
In order to mate this to the tank, we needed a bulkhead fitting of a diameter that would accept the threaded end of this.  Correspondingly, the bulkhead fitting itself had to be a small enough diameter such that the bottom portion of it would fit through the location on the gray water tank where the reducer is installed (shown below).
The bulkhead fitting is a 1.25" size (the 1.5" size was too large to fit into our tank through the reducer opening).  It reads TF-125 and has the word "Banjo" on it.  It is reverse-threaded on its two halves.

DIY HINT:  Whenever you are faced with a predicament like this and you are not sure how to solve it, cobble together your best guess and then take that with you to a specialty seller so that you will have a point from which to begin the conversation.  If you go empty-handed, they might not be able to visualize what you are asking.  My husband put this assembly together and then I took it to an industrial plumbing supply company and asked them if they could think of any ways to improve upon it.  They said, "No - for the purpose you're trying to serve, that's about as close as you're going to get."  
Here's a generalized depiction of how this hydrology functions before and after a relief valve such as this one is installed.  This may be obvious to some folks, but many people have no familiarity with the typical bowels of an RV and so I thought I'd try to convey this with simplified cut-away cartoons:
My husband looked at this cartoon and said, "Just be grateful that our Interstate has separate gray and black tanks!"  No sh*t, pun intended!!

Here is the general procedure for locating and installing this kind of relief check valve on a gray water tank.
Whether your gray tank is installed or de-installed at the beginning of your retrofitting project, you're going to have to mess around under there and find a spot where you've got sufficient clearance beneath the chassis / underside of the vehicle for this thing to fit, because there will be a lot of other junk (wires, lines, pipes, supports, etc.) installed above and around that tank.  Here we had dry-fit our newly-rehabbed tank for the purposes of identifying such a spot.  The chosen location should not be too close to any other tank port (this photo shows a too-close option), and it should not be all the way to either the front or back ends of the tank because those are the areas of maximum slosh while driving.  You don't want to slosh any gray water through the check valve during normal operations.

Once you find a place that seems to work, reach up with a Sharpie marker and scribble on the top of the tank so you can see it later when you take the tank down.  Or mark the spot with masking tape.  
Here you can see my husband's marker scribbles constraining the installation location, and the bulkhead fitting positioned between the lines.  Note that the coring bit on the drill is just a hair wider than the threads on the fitting (in this case, a 2.5 inch bit). My spatially-oriented husband took this pic to illustrate the size of the hole that needs to be drilled in the tank to accept the fitting, not because he was drilling on the fitting itself.  
Action shot - drilling the new hole to receive the check valve assembly.  Best not to screw up this placement because you don't want a do-over here.  
You are going to have to attach the underside of the bulkhead fitting by feeding it in through the side port that receives the reducer fitting which, in turn, leads to the dump valve.  Therefore, that reducer has to come off.  Ours was sealed in place and we simply broke the seal by twisting using this strap wrench.  
Our bulkhead fitting came with a nice large rubber gasket and we suspect it does not have to be sealed in place - a good tightening with a wrench should suffice given that it's on the top of the tank and should see little, if any, submergence.

One wrench on the inside of the tank, one on the outside will achieve the tightening. And then cutting off the extension.  My husband used the PVC pipe cutter shown here but a small hacksaw might have worked better (this pipe is more brittle than PVC).    
Installed, and we did trim off about an inch and a half of the extra pipe above the check valve.

Ignore the confusing stuff in the background of this photo - that is not the Interstate but is rather my husband's antique Mustang restoration project, with one de-installed wheel serving as a convenient Gatorade bottle holder.
We left the assembly at three inches in height because we figured just by common sense that it should be unaffected by sloshing at that height, while still remaining far below the level of the chassis such that there would be no danger of the water backing all the way up to the level of the wet bath.

Stay tuned for Part 3 where we re-install the gray water tank with this new emergency overflow check valve port in place.
And that, ladies and gentlemen, is the Airstream Interstate in a nutshell.  One of the forum users (I forget who) aptly described them as follows:  "As many have observed, the Interstate is brilliantly designed but shoddily executed. If you are willing to work through the shoddiness, you will be rewarded by the great design."  We could not have said it better ourselves, as we keep discovering one shoddy flaw after another.  

BTW, I do not create my blog memes - I find them as-is on the internet (it's all about the keywords).  I consider it a personal challenge to find just the right meme for any given post.  Sort of like the way some ladies can find the perfect flower arrangement for the dinner table.

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