I've replaced a bathroom faucet and want to replace the p-trap beneath it, since the metal tube going into the connector on the wall fell out and is badly corroded on the end. (There had been no leaking.) I cleaned out the pipe as well as I could, but the old nut is solidly connected. I've been concerned about really forcing it and causing major damage to the pipe it's screwed on to. Is it absolutely necessary to remove it? Would I have a leaking problem if I push the new plastic pipe through it and use plumbers putty to seal it up?

What you are experiencing is common. They are pot metal, corrode but are easily cut. Use a hacksaw blade to cut a slot in the old one, carefully remove it, get a new one at HD or Lowe's, they are all the same thread, install a new one and put some plumbers grease on the threads.

The new connector I got when I bought the pipe is lightweight zinc, but the one I have to remove is solid and heavy (and 44 years old). I don't think I can cut it.

Yes, you can cut it. Take a hack saw and cut across the nut. Be careful not to cut into the pipe threads. When you cut half way through the nut - take a chisel, insert it into the cut and gently tap it with hammer. It will break.

If you have a hard time installing new nut on old pipe, then you should get Fernco rubber coupling. Those are made for this type of situations - and must say, they saved the day many times before

Let us know how you did

Milo

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Yes, you can cut it. Take a hack saw

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Use a mini-hacksaw

Okay. I'll try to describe what I'm looking at. (Unfortunately, I can't take a picture of it.) The black plastic pipe inside the wall has an O.D. of 2-1/4" and a smooth surface until it reaches the outside edge of the wall. Then it has outside threads that show beyond the wall for about 1/2". The metal connector I need to remove looks like it may be screwed onto the outside of the threaded pipe, so the pipe is threaded for maybe another 1/2" that isn't visible.

Right now, the metal connector overlaps the inside of the plastic pipe for 1/4" which then overlaps a metal liner that goes into the pipe an additional 1-1/2".

It looks like the corroded pipe I pulled out of the opening was unattached except for plumbers putty. I don't see any evidence of a clamp of any kind. Is that typical? That is why I wondered if I can insert the new pipe into the opening without removing the connector.

The rubber coupling is intriguing. I'm not sure of where the larger end should be attached, since the part of the internal wall pipe that is exposed, is threaded. It may be possible to slip it onto the unthreaded part of the pipe that's in the wall and reach in with a screwdriver to tighten the clamp. Is that the idea?

I hope my details are helpful.

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The black plastic pipe inside the wall has an O.D. of 2-1/4"

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That says you have ABS (plastic) pipe.

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Right now, the metal connector overlaps the inside of the plastic pipe for 1/4" which then overlaps a metal liner that goes into the pipe an additional 1-1/2".

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That sounds like a compression nut on the end of a ABS threaded adapter.

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a metal liner that goes into the pipe an additional 1-1/2"

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That sounds like the remainder of the corroded trap arm.

Get a large pair of pliers (or pipe wrench) and take the nut off. It may be corroded but it is not fused by corrosion to the ABS pipe. That just doesn't happen.

After removing the nut pull out the remainder of the corroded trap arm.

The way this works is, a nut is slipped onto the trap arm, then a beveled washer is put onto the trap arm. The trap arm is put inside the ABS pipe coming out of the wall. The nut and beveled washer are slipped up against the ABS threaded adapter. The nut is threaded onto the ABS threaded adapter and tightened. The tightening of the nut compresses the beveled nylon washer and makes a water tight seal.

I agree with what Harold said. It is always difficult to work deep inside the cabinet with tools. You have to fight it. If that is really ABS pipe then it should be relatively easy to remove that nut. That metal liner fits very tightly into ABS pipe. Loosen the nut a bit, take pliers, grab the end of the "liner" and pull it out. Remember: larger tools you use - the more leverage you will have - the easier it will go.

Back to you

Milo

I finally was able to unscrew the metal connecting nut. The metal liner I mentioned earlier that is inside the ABS pipe is a uniform depth of around 1-1/2" and not corroded at all. I can't grab it to pull it out, since the open end of it is flush with the ABS pipe opening. I tried pulling it from the back of it with a tool that has a small hook on the end, but can't get it to budge. (Sound familiar?) The inside diameter of the metal liner is 1-3/8" so it's not part of the original 1-1/4" corroded pipe. The new pipe going into the wall is 1-1/4" like the old one. Now I'm back to the original question, more or less. Is it necessary to remove that liner in order to install the new pipe or would it work to get an identical connector and use plumbers putty on the inside in addition to the washers that come with the connector and on the outside where the connector surrounds the new plastic pipe? The new connector I bought would fit the new pipe, but not the ABS so I'd have to get a different one. If that's the case, would a plastic connector be better than a metal one? The old corroded wall pipe seems to have extended into the opening about the same depth as the metal liner.

If you don't remove the metal liner, you won't be able to insert new pipe into the fitting. Without seeing photo of your situation - what is happening, you have 1 1/2" to 1 1/4" ABS drain adapter sticking out from the wall. This adapter will accept the liner only to a certain depth until it hits the pipe reduction half way in. That liner is snug inside that pipe but is not glued or held by any other means. I suggest again - try to take it out. ( Take skinny flat screw driver, place it between the metal liner and ABS pipe, bend it inward and continue around the diameter of the liner until it gets loose ). If you don't remove it than you will have to most-likely use Fernco coupling that install on the outside of the pipe with s.s. clamp.

Again: Do not use Plumbers' Putty or Caulk to make the seal as these two compounds are not designed or used for that purpose.

Back to you

Milo

There's no clearance whatsoever to allow a skinny screwdriver or even the point of an X-acto blade to locate a gap between the ABS pipe and the liner. The outside diameter of the ABS pipe is 2-1/4". The inside diameter of the liner is 1-3/8" and the new pipe outside diameter is 1-1/4" and goes into the liner with room to spare. If I locate the necessary Fernco coupling, I assume it should go far enough into the wall to be attached to the part of the ABS pipe without threads and beyond the wall opening.

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The inside diameter of the metal liner is 1-3/8"

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The new pipe going into the wall is 1-1/4" like the old one

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Will the new pipe (trap arm) fit inside the metal liner?

Sounds like someone really mucked this up sometime in the past.

Traps come in two sizes. The 1 1/2" is for kitchen sinks. The 1 1/4" is for lavatory sinks. Sounds like someone put in a 1 1/2" trap adapter for a lavatory sink. Or they used a regular threaded adapter which is not the same as a trap adapter. Then rather than correct it tried to make some jerry rigged contraption by putting a short piece of 1 1/2" trap arm inside the trap adapter.

If the new trap arm will fit inside "metal liner" get a new nut and 1 1/4" beveled washer. You may have to buy a 1 1/4" trap adapter to get the nut and washer. The nut should be the same size as the nut for a 1 1/2 trap adapter.
Go to Home Depot or Lowe's, find a 1 1/4" trap adapter and a 1 1/2" trap adapter. Switch nuts to see if they are the same.

If the nuts are interchangeable, buy the 1 /14" trap adapter. Put nut and washer on your trap arm and slide inside the "metal liner" and tighten the nut.

Note what I said above. A regular threaded adapter is not the same as a trap adapter.
The trap adapter will come with the nut and beveled nylon washer. Also you probably will not be able to find an ABS trap adapter, get a PVC. You will not be using the adapter itself, only the nut and washer.

Please, post a clear photo of this pipe with liner - so we don't have to keep guessing. Thank you

Milo

The new trap arm (wall tube) is 1-1/4", just like the old corroded one, and slips easily into the 1-3/8" inside diameter liner (that I can't remove) with room to spare. The old trap arm apparently was held in position with the 1-1/4" metal connector that I finally removed, which screwed onto the outside threads of the ABS pipe where the trap arm enters. I can easily take the old connector nut and washer to the store and match it up, if that's all that's needed. This may have been done 44 years ago in a way that's not typical, but it's held up all this time without a leak, so maybe I've been lucky. I'm not able to provide a photo.

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I can easily take the old connector nut and washer to the store and match it up, if that's all that's needed.

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Well it only cost you $2 and 15 minutes to try it.

Are you done yet?

Thank you for your help.