Rubber donut instead of threaded bushing?

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Jfenn

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I encountered an unexpected obstacle in the course of adding a washer hookup to an existing sink drain. My original post is here:
Thread 'Adding Washer to Existing Kitchen Sink Drain' https://terrylove.com/forums/index.php?threads/adding-washer-to-existing-kitchen-sink-drain.98440/

Turns out that the iron bushing that was threaded into the side of the cast iron stack is 3.5". So I cannot use a threaded 3" or 4" PVC fitting. I can get an iron 3.5" to 3" threaded bushing from a plumbing supplier for about $43. I also found a rubber 3.5" to 3" donut at a big box store for $7. The existing threads in the cast iron stack are rough as a cob. The original bushing was threaded in only a couple of turns. All the threads after that are covered with corrosion.

My question is: Should I pop for the iron bushing, or will the donut work (assuming I can get it and the 3" drain pipe into the fitting)?

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WorthFlorida

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I'm not a plumber but I'm not sure if those donuts are not for threaded fittings. If you go with the treaded fitting, use a wire brush to clean the old threads inside the clean out.

From Furnco description:
These donut shaped rings are for compression sealing for sewer pipe joints and drain waste and vent connections such as sockets, hubs, bells and spigots.
 
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Mr tee

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Back in the dark ages I made a few 3 x 3 1/2 ABS spigot x mip adapters by reaming out a 3 1/2" plug until a chunk of 3" pipe fit in snugly and cemented it in place. Of course this was not a legal fitting, you are not supposed to build your own fittings. 3 1/2" indicates it is a cleanout for a 4" line and even if you add a 3" cleanout that would be undersized, another problem. This would also be a problem if one used a threaded bushing. However, I seem to recall that some specialty company (who?) came out with a fitting like the one I made. But, that was decades ago and the sales volume must have been tiny so I doubt they are still out there. But, to answer your original question, a donut won't work.
 

Terry

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I would pick up the threaded bushing. If that doesn't work, you might be looking at removing the fitting where it goes into the leaded hub, and doing a replacement there. That would involve a donut or a lead pour, and then a shielded coupling higher up the line.
I would try the threaded bushing first I think.
 

wwhitney

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What about the issue that the cleanout-tee does not have the curvature of a san-tee? A problem in practice, or just a code violation that is still likely to work well?

Cheers, Wayne
 

Terry

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What about the issue that the cleanout-tee does not have the curvature of a san-tee? A problem in practice, or just a code violation that is still likely to work well?

Cheers, Wayne

Well, I haven't been doing that on a cleanout before. The best would be to cut out what is there and start over with a santee, and a cleanout above that.
 

Reach4

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A 3.5 inch plug thread would have an OD of about 4 inches at the biggest in the threads. The ID of the female thread would be reduced by the thickness of the threads. A hub for 3.5 inch might have an ID considerably different than 4 inches, and that donut would be made to match that hub. If I were a plumber, I would avoid doing non-standard things considering that you can take on liability (often unfairly) by doing non-standard things.
 

Jfenn

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I'm not a plumber but I'm not sure if those donuts are not for threaded fittings. If you go with the treaded fitting, use a wire brush to clean the old threads inside the clean out.

From Furnco description:
These donut shaped rings are for compression sealing for sewer pipe joints and drain waste and vent connections such as sockets, hubs, bells and spigots.
Thank you for your reply. I bought a 4" wire wheel brush and was able to get it inside the threaded opening and got the threads clean up to where the old fitting had been screwed in. After that point they're a mess. I've decided to go with the more expensive option of the threaded bushing as it seems failproof if used with a generous application of thread sealant.
 
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