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Old 08-06-2011, 05:23 PM   #1
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Type of plastic in waste tanks

The black water tank on my 75 TWind has a hairline crack on top, running into where the crapper fitting threads in. I'm pretty sure I can do a succesful hot weld on it but I need to know what type of plastic it is. I was looking at some old posts and some say it is ABS, others say polyproplyne. Anyone know what they used?

Thanks, Paul
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Old 08-06-2011, 06:17 PM   #2
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It's a form of ABS. I have been able to repair a crack in one, using an old milk jug for additional material.
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Old 08-06-2011, 07:20 PM   #3
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I'm a little suprised it's ABS. I never knew ABS could be flexable like that. I have a hot air welder that works well, but you have to be sure to use the correct rod.
Thanks for the info.
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Old 08-06-2011, 07:30 PM   #4
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I got the same problem on what is probably the same tank. I'm not going to mess with it. I'm told that you can still get one from Inca, although, their web site is currently messed up...no catalog info.
Anyway, from seeing how the whole arrangement is put together, it seems inevitable for it to fail. When anyone sits on the throne, all the weight is put right there on those threads; there's nothing really supporting anything.
a slab of plywood sitting across the top of the tank? really?
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Old 08-07-2011, 07:33 AM   #5
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I have to agree, it is a strange way to support the toilet. I would say the tank has been cracked for some time by the looks of it. I don't think it will leak if it doesn't get worse. I'm thinking since I've got everything taken apart, I would stop drill the crack and do a weld. I'm more concerned about fumes seeping out than anything else.
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Old 08-07-2011, 07:48 AM   #6
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I have to agree, it is a strange way to support the toilet. I would say the tank has been cracked for some time by the looks of it. I don't think it will leak if it doesn't get worse. I'm thinking since I've got everything taken apart, I would stop drill the crack and do a weld. I'm more concerned about fumes seeping out than anything else.
I had the same concerns with the one I repaired. I simply drill stopped the crack, and melted the crack, along with a clean milk jug, with a heavy duty soldering iron.
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Old 08-07-2011, 08:03 AM   #7
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Yeah, it won't "leak" unless you roll the trailer. (or over-fill). But I suspect that this is the reason that I get a huge blank-tank smell inside the trailer whenever I empty the tank. I always thought it was (possibly) due to the fact that I have no grey tank, and there's a straight path from the shower drain to the sewer drain; the grey pipes connect just south of the black tank valve. (if you were to leave the sewer cap on, and pull the dump valve, black water would back up this shower drain, and fill the shower pan). So I just thought fumes were backing up there. And yes, the shower has a p-trap, but I assumed that the water in it got jiggled out on the ride from the campsite to the dump station. (I'm sure this is partially true, because whenever you take the cap off the sewer hookup, a little water comes out.)

Anyway, I just dismantled my trailer, and the shower trap was full. after driving all the way home from the last camp out. so, that ain't it. Its probably that crack, and the big whoosh of air that goes into the tank when dumping, stirs it all up and it wafts into the trailer. The tank is covered up on the top by the tank cover, but its open on the sides, going into the closet and under the vanity.

Considering the difficulty of accessing the tank, I personally wouldn't want to risk a repair failing. Then again, I'm not confident that a brand-new replacement would hold up any better. ({sigh} decisions, decisions...)

I'm still leaning toward not replacing this tank, but instead, installing a 25 gallon tank below the floor. In place of the original tank, I'll put a plywood box (or "table), to support everything, but still be able to use the original bathroom fixtures. Then put a 6" riser pipe from the sub-floor tank up to the toilet. This would be covered by the original tank cover, so from the inside, it'll look like it always did.

I've mentioned this idea in a couple of threads, but haven't gotten much feedback on it...never seen anyone else do this. Gotta make a decision soon, though, as I'm about ready to actually remove the plywood floor.
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Old 08-07-2011, 08:51 AM   #8
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Here is what I am working with.
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Old 08-07-2011, 09:03 AM   #9
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I've used a plastic weld by epoxy that works really well on any type of abs plastic or pvc.
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Old 08-07-2011, 09:07 AM   #10
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I have not used the coach enough to know if I have a smell problem at this point.

I am at the same point as Chuck in the rebuild. I'm just about ready to pull the black tank and replace the floor. I'm sure replacing the tank is the prudent thing to do, but I'm not made of money either.

I think Purman and Overlander are on the right track. Do a repair.

Question for Chuck: Have you tried sealing off the shower drain with tape or something, dumping the black tank and seeing if you still get sewer gas? Could a black tank dump suck the water out of the shower p trap? If not and there are no leaks below the floor that would only leave a leaking vent? I'm not a plumber so that is just a guess.
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Old 08-07-2011, 09:28 AM   #11
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Have you tried sealing off the shower drain with tape or something, dumping the black tank and seeing if you still get sewer gas? Could a black tank dump suck the water out of the shower p trap? If not and there are no leaks below the floor that would only leave a leaking vent? I'm not a plumber so that is just a guess.
The only vent should be in the roof of the trailer, which is where the air should come from, no shower drain sucking involved. Any odor will be from inside the trailer.
Oh, we get a sewer odor when our black tank is about 1/3 full, with no leaks. It may just be "the way it is".
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Old 08-07-2011, 09:47 AM   #12
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Here is what I am working with.
That crack was caused by vibration.

I am not sure that you can successfully repair the threads.

Andy
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Old 08-07-2011, 09:55 AM   #13
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The tank is not ABS. Plastic milk bottles are High density Polyethylene, just like the tanks. If you have a hot air welder. Much like a hairdryer on steroids. You can melt the tank locally and add in filler rod of Polyethylene. There a lot of places that do this professionally. In the process of welding you will anneal the tank locally so it will not crack again, if it is done right. You can also buy one of these hot air welders for more that it would cost you for a new tank.
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Old 08-07-2011, 10:12 AM   #14
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Question for Chuck: Have you tried sealing off the shower drain with tape or something, dumping the black tank and seeing if you still get sewer gas? Could a black tank dump suck the water out of the shower p trap? If not and there are no leaks below the floor that would only leave a leaking vent? I'm not a plumber so that is just a guess.
yeah, a rubber stopper in the shower drain. doesn't seem to make a difference.
maybe it is just "the way it is"...but I'm not talking normal little whiffs, like when you flush the toilet, and a little air can leak up into the cabin. I'm talking only when dumping.

your tank looks different than mine. I don't have that formed bump; the tank top is totally flat.

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