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Old 01-02-2015, 07:53 PM   #1
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1971 31' Sovereign
Indian Wells , California
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Black tank toilet plastic piece

On my new-to-me '71 AS Sovereign, I noticed the original Starlight toilet rocked a little bit. I removed the toilet and unscrewed the flange. It looks like the white plastic piece that is glued to the black tank has lost its grip on about half the circle. The tank has two very small cracks at about the 2:00 and 7:00 o'clock positions, about ˝ inch long.

I'm planning on changing out the toilet to a Bravura because at some time someone threw a cigarette in the toilet and it burned the bowl. If it wasn't for that I'd probably change the seals and keep it.

Is there some kind of glue I can use to stabilize the cracks and bond the plastic circle back on the tank?

Thanks!
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Old 01-02-2015, 08:40 PM   #2
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May be a plastic welder for the cracks, silicone for glue,,
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Old 01-03-2015, 07:07 AM   #3
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Only use silicone approved for aluminum. Jim
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Old 01-03-2015, 08:14 AM   #4
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Being the fact that the tank is plastic, I would use something for plastics. I had leaks in my water tank at the fitting for the drain and the fitting going to the water pump. I used JB Weld, which is an epoxy 2 part. Excellent adhesion and sealing, no leaks. I highly recommend it!
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Old 01-03-2015, 06:56 PM   #5
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I'm just guessing. I'll bet the tank is a roto molded polyethylene thermo plastic material. Cracks in the tank can be welded, more like brazing. I'm sure there are You Tube videos showing the technique.

I have never known an adhesive that would adhere to polyethylene.

My new black tank came with a 3 1/2 toilet "sealing grommet". I used a hole saw to cut a 3 1/2" diameter hole in the tank and then inserted this grommet in the hole. Then I inserted the toilet flange into the grommet which provides a good seal. The toilet flange is then screwed to the subfloor. You can see the grommet and toilet flange in the photo below. It might be a way to "rebuild" your toilet connection for a new toilet.

The weight of a human on the toilet seat must be absorbed by the subfloor. The plastic black tank ain't strong enough to take that weight. If your john is rocking, I wonder if there is a problem with the subfloor around the toilet.

David
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Old 01-03-2015, 07:41 PM   #6
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I have had good luck heat welding thermoplastic. Harbor Freight even has an electric welder and filler rods. the trick is to get the heat deep enough just like welding metal. Practice a bit on another piece, Tide bottles have been used for filler also along with a large electric soldering iron 75-100Watts.
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Old 01-03-2015, 08:23 PM   #7
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The tank is a soft black plastic. I expected it to be hard ABS.

Luckily the subfloor is solid. The reason it rocked was the screws for the flange pulled out of the wood subfloor allowing the toilet to rock forward but not backward.

The two cracks in the tank are very short, less than ˝ inch. My bigger concern is how to get the white plastic piece glued back to the tank. If I move the flange screws, the new toilet won't rock anymore. The factory glue looks like it's grey but I have no idea what they used back then.

I think JB Weld is probably the way to go with a clamp to let it set overnight.
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Old 01-04-2015, 07:12 AM   #8
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Good Morning CraigCA. It kinda looks like the white plastic piece is some type of sealing "ferel". I wonder if the spherical shape mates with a similar female shape on the bottom of the flange. It looks like it may fit in the groove on the bottom of the flange. Maybe the white plastic piece was calked to the tank, and then drawn tight when the flange sits on top of it. I work in a roto molding factory making polyethylene tanks and do not know of any adhesives that will adhere to this type of plastic. But we have made lots of repairs by "welding".

You have discovered the reason for the rocking toilet. Now you have to figure out how Airstream wanted the toilet flange to seal to the tank, and how Airstream wanted the toilet to seal to the flange.

David
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Old 01-04-2015, 09:37 AM   #9
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dbj216- On your new tank, does the flange slip into the tank and then screwed to the subfloor? That's what it looks like. The toilet flange I removed screws into the white plastic ring that's glued to the tank. You can't see the threads but you can see the Teflon tape on the flange threads. From what I read here this is how it came from the factory.
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Old 01-04-2015, 10:18 AM   #10
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Okay. Maybe Airstream and others were using threads to seal the flange to the tank. That white piece sure looks like it has a sealing spherical shape to it that may have been designed to tighten against the groove in the toilet flange.

I purchased my tank, toilet flange, and grommets from Inca Plastics in California. They have been making RV tanks forever. I think of them as a pioneer in the rotomolding process.

The rubber grommet has a deep groove around the OD that is the thickness of the plastic tank. The grommet is forced into the 3 1/2 hole in the tank and messaged to fit into the groove. So we have a rubber flange on both the inside and outside of the tank. The tank is then hung under the subfloor. Next the hard plastic toilet flange down pipe is cut to the right length, subfloor to bottom of grommet. I lubed the down pipe and pressed it into the rubber grommet. It is designed to be a press fit. This forces the grommet to seal hard against the hole in the tank. Last, I mounted the flange to the subfloor. This system makes a permanent seal of toilet flange to tank with no forces on the seal other than travel vibration. Note, it might have been a 3 3/4 hole. I can't remember exactly.

My new Dometic 310 toilet came with a soft rubber gasket that compresses on the toilet flange when the toilet is bolted down with the standard T bolts. There is a short toilet down pipe that fully engages the toilet flange ID. I attached a photo of the flange sitting in the grommet with the flange screwed to the subfloor.

One attachment technique we use in our tank factory is called "spin welding". This process was invented years and years ago by Inca Plastics. It is friction welding. This is the way we attach plastic threaded fittings to tanks. We spin the fitting in a router and press it into the hole in the plastic tank and friction heats the plastic and the part mushes into the tank. Maybe that is how the threaded plastic fitting was attached to your black tank. I think I see four little "nubs" on the white plastic piece that might have been drive dogs for a spin weld process. Again, just speculating.

Here is a picture of my old Trade Wind black tank with flange. It had a lot of cracks in it. The flange is very rusty and pitted. It is not a rotomolded polyethylene tank. It is a two piece tank with the flat top welded to the formed bottom.

David
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