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Old 07-27-2013, 02:06 PM   #1
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Black tank water backing up into shower pan!

Hi all, we have a '66 Caravelle. It has one black tank, no grey water tank. It appears the black tank contents are backing up into the shower pan! Yuch!

How can this happen? Isn't there some kind of flap or something between the black water tank and shower?

According to the diagram in our manual, the water should all flow 'downhill' from kitchen sink, bath sink, shower into the black tank, not vice versa.

We tried forcing water through the two vents on top and the water flows out the black tank drain ok.

Then we capped that and filled the black tank with water through the toilet bowl, as soon as it was full, water started backing up into the shower pan, leading out the cap and leading out of the shower trap.

Has anyone experienced this or do we have to drop the belly pans and replace the whole black tank?

Thanks for any advise!
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Old 07-27-2013, 02:10 PM   #2
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Nothing flows into the black tank except black tank contents from the toilet. Everything else dumps directly onto the ground, and if you cap off the end of the pipe, it will back up into the shower and tub.
Besides, doesn't the black tank sit on top of the floor? So the contents would be higher than the bottom of the shower? First rule of plumbing: Left hot, Right cold, and poop flows downhill.
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Old 07-27-2013, 02:23 PM   #3
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At some point the output of the black tank has to join with the gray water coming from the shower so it can go out a common pipe to the sewer hose. Normally the black tank doesnt stay open till you open the dump valve and should not back up since it is a bit lower and farther along then the gray water. If the dump valve is open and the sewer output is blocked, it will backfill the common piping and that could cause black water to come up in the shower. Another possibility is that it is somehow overfilling and then it is backing up through the vent piping and from there getting back into the gray side plumbing and into the shower. Either way, if the dump valve is open and the hookup to the sewer hose is fine, it shouldn't happen.

Keep in mind that the black tank on older trailers isnt very big so it may not take all that much to fill it up. And if it fills up and the dump valve is closed, it has to go somewhere.
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Old 07-27-2013, 02:54 PM   #4
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Hi guys, thanks so much for the quick replies! Yes the black tank sits atop the floor, the toilet atop of that, so we would think that toilet contents drop directly into the BW tank. So I guess the problem is that it's not very big and if we are not hooked up and 'flowing', then we have to watch for it backing up into the shower.

Anyone know how big the tank is? The manual doesn't say. From what little I can see of it through the closet, it looks like it may be about 3 gallons or less.

So our only solution really is the mobil blue tank for dry camping or always being hooked up for RV park camping it seems.

How would they have dumped 'grey' water directly to the ground, by removing the shower trap drain plug and letting it flow out there?

Has anyone installed that gray tank that VTS sells? If so, what are the difficulties encountered? Does it come with good instructions? Would we be able to block the BW tank completely from the gray pipes then to avoid a back up in the future?

Our original BW tank guillotine doesn't work (it leaks). Has anyone ever replaced the guillotine slide on the orginal black tank? Can you get at it if you drop the belly pan or is it above the floor too?

We tried one of those 'replacement' guillotines that attaches to the sewer outlet but it's leading too (brand new)! Geez.
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Old 07-27-2013, 02:54 PM   #5
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It has one black tank, no grey water tank.
Do you mean one combined tank for everything? If that's the case, then when that one tank is full, it's only natural it would back up into the shower pan, as that's the location of the lowest drain opening.

There are no check valves on the sink and shower drains to prevent back-flow. There may be a trap (an "S" shaped bend in the drain line, so a little bit of water is trapped in the line to prevent the drain from serving as a vent) but that's it, and even that is not necessarily a given.
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Old 07-27-2013, 03:06 PM   #6
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Originally Posted by awolff View Post
(snip)

Anyone know how big the tank is? The manual doesn't say. From what little I can see of it through the closet, it looks like it may be about 3 gallons or less.

Our original BW tank guillotine doesn't work (it leaks). Has anyone ever replaced the guillotine slide on the orginal black tank? Can you get at it if you drop the belly pan or is it above the floor too?
The black water tank on your Caravel is about 12 gal.

The reason you are getting black water into your shower appears to be that your black water tank valve is not working (leaks) and you are caping your outlet. That means that your black water tank is leaking back into your gray water lines and coming up in the shower.

You must replace the leaking black water valve at the black water tank. One at the outlet will not work as it will cause the problems you are having. The leaking valve lets black water into the gray line.
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Old 07-27-2013, 03:16 PM   #7
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Ah, Idroba, so when you say 'black water tank valve', you must be talking about the guillotine valve that we have that opens/shuts from inside the bumer compartment, right? I don't know of any other valve. And the adapter one we bought will not solve this problem.

Can we get at the original guillotine from underneath when we drop the belly pan? We had the belly pans off of it once, but didn't notice the guillotine, though, at the time, we weren't really looking closely at the plumbing (now we know we should have!). And any ideas of where to find a replacement guillotine valve? Didn't see one at VTS.

Thanks for all the advise!
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Old 07-27-2013, 03:29 PM   #8
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When I had my Caravel (a '67) I never had to remove the bellypan or work on the slide valve, so I can't help you there. But others have had experience I am sure and may be able to assist you on just how to best get at it. And yes, I am talking about the guillotine valve that is at the bottom of your black water tank. And no, the adaptor valve you bought actually created the problem in your original post by plugging the outlet up and causing the leaking water to go into your gray water lines, then back into the shower.

The original slide valves were Thetford's and should still be available at a well stocked RV supply place or on line. You may be able to just replace the guts of the valve, again, I have never had to do that, but I think replacing a Thetford with another Thetford would be much more advisable than trying to substitute a Valtera (sp) which is the most common one used today. So, get a Thetford, after you expose it and can see just how it is attached. I would think that VTS would have them, as would Inland RV, or Out of Doors Mart, or any Airstream dealer. You may have to call them to get just the right valve.

It is always a yucky problem to work on the black water tank, but the final results will be worth it. Enjoy your Caravel.
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Old 07-27-2013, 03:44 PM   #9
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Thanks so much, we'll drop the belly pan back there and take a look. So in conclusion, if i have it right, the original guillotine is between the BW tank and the grey water pipes and would normally stop BW from getting into the GW pipes, but it's leaking. Correct?
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Old 07-27-2013, 03:55 PM   #10
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Thanks so much, we'll drop the belly pan back there and take a look. So in conclusion, if i have it right, the original guillotine is between the BW tank and the grey water pipes and would normally stop BW from getting into the GW pipes, but it's leaking. Correct?

You are correct. That leaking valve is causing your problems. I had Uwe at Area63productions install a seperate gray water tank in my 65 caravel so I wouldn't have to carry a blueboy around to handle the greywater. Still using the original black water tank and valve for the sewage.
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Old 07-27-2013, 04:12 PM   #11
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Awolff,
Also keep in mind that when your hooked up at a campground, you need to leave your black tank valve closed until its near full or your ready to leave. You need to keep the liquid in there to help flow the "solids" down the pipe, with your leaking valve you will just end up with a big "solid" mess in the tank.
Your gray water exits the trailer past the black tank valve, so you may have to use a portable tote if your not hooked up.
Your black tank valve needs to be fixed, and you will need to open up the belly pan to get in there, and I would switch it over to the new valterra fitting.
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Old 07-27-2013, 06:10 PM   #12
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Seldencove, thank you! I did not know that! I thought we should hook up and let it flow!

Funny, i always thought the gray water was routed 'into' the black water to help keep water in that tank or something. It all makes more sense now! Wish I'd had xray vision so I could see the piping under there.

You have all been so very helpful, i love this site!

Does anyone know if there's a thread on fixing the valve and switching to the new valterra fitting?
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Old 07-27-2013, 07:15 PM   #13
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Seldencove, thank you! I did not know that! I thought we should hook up and let it flow!

Funny, i always thought the gray water was routed 'into' the black water to help keep water in that tank or something. It all makes more sense now! Wish I'd had xray vision so I could see the piping under there.

You have all been so very helpful, i love this site!

Does anyone know if there's a thread on fixing the valve and switching to the new valterra fitting?
Modifying the system, will make you obsolete to the industry.

Keeping the system original, will allow you to communicate with dealers that know Airstreams.

Other wise, you will be all by yourself.

Also, plastic changes dimensions in time.

Rebuilding a 40 plus year old valve, is very risky.

Andy
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Old 07-27-2013, 07:24 PM   #14
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If the handle is in the trunk. Can you see the dump valve by looking into the trunk behind the handle.
I was able to replace the one on my Argosy thru the trunk. No belly pan removal required.
If you do not want to install a grey water tank. You can use a portable tote like a Blue Boy to handle the grey water.
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