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Old 04-04-2018, 06:03 PM   #1
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2002 25' Classic
Portland , Oregon
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2002 black tank leak- what's the likely culprit?

Hi friends,

I have developed a slow leak from the black tank on my 2002 Classic, near the drain. I am guessing that it is where the drain connects to the tank. I am not able to remove the belly pan- afraid of opening a can of worms there, so taking it to an AS repair shop soon.I asked if they do plastic welding at all and they don't, especially if it is a crack in the tank. I have to travel 1.5 hours to get it to them, and would not be a happy camper if this repair ends up costing big bucks. What is involved with replacing the drain pipe??
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Old 04-04-2018, 07:28 PM   #2
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2004 28' Classic
Monument , Colorado
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It is not a big deal if the bottom pan has already been cut out so they can access the plumbing. Maybe two hours of labor and $60 to $100 in parts depending on the issue. If the pan has not been cut out already, add another 2 to 3 hours of labor to the project. If it really is the tank leaking, I don't have an estimate, but a lot more.
2004 Airstream Classic 28 "Willard"
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Old 04-04-2018, 07:29 PM   #3
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The other "got you" is it takes a couple of weels to order the replacement tank. A couple of folks have posted they were able to repair leaks where the piping attached, so you may get by with a fix. We were not that lucky as our failure took out the tank. Pat
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Old 04-04-2018, 07:58 PM   #4
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1986 34' Limited
1975 27' Overlander
Conifer , Colorado
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Unfortunate, but not uncommon, to have to drive quite a ways to see an Airstream tech. Do the tech a favor and dump and flush that tank a couple of times. Take it to the tech with the tank empty.

Here are some reasons a black tank would leak "near the drain".

1. The blade valves that we use to dump the holding tanks are connected to the black tank with sealant and a hose clamp. A leak can develop there.

2. Blade valves can get debris stuck in them preventing the blade from fully closing. Usually new seals in the valve will fix the problem. A new blade valve with fittings is less than $30. Leaky blade valves leak out the sewer pipe, not onto the ground, so that's not a likely cause, unless the valve is actually comming apart.

3. The toilet is connected to the black tank via a floor flange and some type of seal, usually a 3" threaded seal. The attachment fitting is usually "spin welded" to the black tank. I've seen these spin welds fail as it did on my old Overlander.

4. I have seen the molded boss where the pipe is connected to the tank crack from age and vibration. This can be a source of the leak also, although quite unusual. Cracked tanks are usually replaced.

5. Maybe there is a leak in the 3" ABS sewer pipe from the dump valve to the drain port. Something like a crack from road debris, or a loose flex coupler if one is used in the piping.

I just installed a new black tank in my old Overlander. This included a new toilet connection and sealed floor flange, and new dump valve, and the new tank of course. Big project for me. Belly pan had to be removed. I renewed the dump valves on our 86 Limited. I had to drop the tank pan to gain access to the valves.

Labor rates in an Airstream shop will be over $100 an hour. They should be able do diagnose the leak problem and give you a solid estimate of the repair cost and completion date.

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Old 04-05-2018, 09:24 AM   #5
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1996 34' Excella
Elberta , Alabama
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Look at this in a simple way, before thinking about potential big problems. My guess is that the Thetford valve on the blackwater tank is probably the time you buy replacemnt parts to rebuild the valve, you might check to see the cost to replace it with a new valve.....there are better valves out there than Thetford..
Good luck,
Old age is coming at a really bad time!

1996 34' Excella 1000, interior totally redone, 2003 Dodge/Cummins HO, U.S. Gear exhaust brake, Diablo tuner, 115 gallon aux fuel, Bedslide, Airsafe/Reese Dual Cam, and a bunch of other stuff
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Old 04-05-2018, 10:17 AM   #6
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2000 30' Excella
Toledo , Ohio
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Mine was leaking and all it was ,there is a o ring seal between the valve and the adapter to the tank. But I replaced both valves since mine is a 2000 model year . not a bad job if you don't mind laying on your back and have the tools . worst part was cutting access hole in the tank pan .
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Old 04-05-2018, 03:21 PM   #7
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2002 25' Classic
Portland , Oregon
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Thank you all so much for your advice. I will report back after the repair is done
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Old 04-05-2018, 08:04 PM   #8
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billings , Montana
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Not a bad job to remove the belly pan....
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Old 04-05-2018, 10:06 PM   #9
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1995 25' Excella
xxxxx , xxxxxx
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I am betting the adapter that connects your dump valve to the tank is cracked. My gray and black ones cracked at about the 20 year mark. I consulted my owners manual. It said when the valves needed service, the dealer would cut a hole in the belly pan, make the repair, and put on a cover plate...That is exactly what I did...I bought a set if shears from Harbor Freight and zipped out a hole. I ordered new valves and adapters. I bought the other pipe and fittings at a hardware store. I put in the new set up, then got an old street sign to make a cover panel. The job probably took me 6-8 hours including the trip for pipe. It took me so long because I dragged out every tool in the garage trying this and that. Now with an access panel and some knowledge, I could probably do the job again in and hour or two....My total cost was under 200 bucks, not counting the shears.
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