Will thin wall pipe collapse when torqued?

Re-piping a bathroom lavatory drain. The original has a short stub pipe screwed into the waste pipe, and to that stub, a 90 degree ell connecting to the trap.
In the new configuration, I must remove the ell, and run a horizontal straight into the stub, sealing it with the conventional plastic ring and screw ring. The stub has been there about 30 years or so, and the pipe wall is much thinner than the stub replacement I bought today. The pipe end is rusted and damaged, and while that made no difference with the ell, it will not make a seal with the plastic ring. I need to remove the stub and replace it. When I bought the parts just as the supply house was closing for the day, I asked about removing it and the plumber there said yes, just put a pipe wrench on it and jump up and down on it and eventually it would break loose. I was all ready to do that tonight until I discovered the thin wall of this pipe.
Does anyone know if there is a danger that an old, thin wall galvanized pipe about 1 1/2 to 2 " diameter is likely to collapse under the torque of a heavy handed use of a pipe wrench? It seems like it might. If it is possible, and does collapse, is there anyway to remove the stub at that point. I would like not to have to tear out the wall that is all ready for finish painting and completing this redecorating project. (Is there a way to get around removing by screwing on some type adapter that is short and will leave me room to complete the drain pipe to the la? Since this is a holiday weekend, it would have to be something available at the Home Depot or some similar outlet. as supply houses are closed.)
Thanks Sandy
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Sandy wrote:

Yes, it's likely it will break off.
There is a rubber coupling made just for this and it's possible HD carries it. A large hardware store may have it too.
The actual trade size of the pipe will be either 1 1/4" or 1 1/2". The trap is tubular size 1 1/4" for a bath lav. You can saw the galv pipe to the length needed with a hacksaw.
Jim
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Speedy Jim wrote:

Thanks for verifying my concern even though that is not the answer I was hoping for, i.e., that it would likely break. . I will look today for the rubber coupling. I wonder if I don't find that, would it also work in a drain application where there is no pressure, to assemble this with the plastic ring seal, screw everything up tight as possible, and then seal around the stub pipe and the lav tubing with clear silicone caulk? It has to look neat because it is behind a pedestal sink. I guess I could wrap some aluminum duct tape around the rubber collar and stub and it would look very much like the rest of the chrome.
Sandy
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Sandy wrote:

Yes, you can seal it with duct tape and silicone.
I didn't realize this was behind a pedestal <ugh>. That's the kind of app where you don't really want to have to do it all over again next year.
I know it's not what you want to hear, but if it were mine I'd rip out the galv and do it all over as a permanent job. If the stub breaks off trying to unscrew, you can saw (lengthwise) thru the threads left in the fitting to get the piece out.
Your call. Decide if you look forward to taking the pedestal out again in the future...
Jim
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Speedy Jim wrote:

Went to HD and found a brass fitting that screws on to the galvanized stub, and the other end is complete with a Chrome ring and brass ferrule to accept the 1 1/4 pipe. Overall length is only 1 1/2 inches so it will work fine as a permanent fix. The old thin wall will work with despite the jagged edge. I will have a brass fitting in the middle of otherwise chrome, so maybe I can paint it silver someday.
    I agree about the pedestal (ugh). The original lav was wall hung. The space is too tight to fit any but the smallest cabinet, so I thought the pedestal would look better and give a roomier feel. In any other situation I definitely would not use one. Nightmare to install and plumb.
Sandy
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Fernco makes an adapter just for this purpose. Their part no. PDTC-150. It's a small gray rubber like part the connects 1-1/4" to 1-1/2" tailpipes from the sink to 1-1/2" pipe, plastic or metal. I bought one last weekend at Home Depot.
RB
Sandy wrote:

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Thanks RB, See my reply to Speedy Jim. I found a special fitting at the HD before your response, and I did not see the part in our HD that you refer to. Thanks for the suggestion.
Sandy
RB wrote:

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