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johnL
connecting plastic and metal plumbing

Our house is 40 years old so all our plumbing is metal. We had to temporarily remove a bathroom cabinet that houses the sink, and I tried to reconnect everything tonight. The cabinet is definitely not 40 years old, and the drain plumbing is plastic down to, and including, the trap. The part of the drain that comes out of the wall is metal (chrome) with a captive nut that screws onto the threads on the trap.
That connection between the metal and plastic insists on leaking. It did NOT leak before I took it apart. I tried connecting it without teflon tape, I tried a normal amount of tape, and I tried a LOT of teflon tape. (It had teflon on it when I took it apart.) I tried just making it finger tight, and I tried using a wrench (first a little, then a lot).
What's the trick to getting the metal-to-plastic connection to not leak?
Thanks a lot.

dj1
Re: connecting plastic and metal plumbing

Check the thread on the trap. With a captive nut, or when you have a slip joint washer, teflon tape is not needed, and if there was teflon tape before, it's a sign that it leaked before.

If the thread on the trap is damaged, replace the trap.

If the thread on the trap is fine, replace the waste arm. I prefer ABS.

With any sign of a leak, it's a good idea to replace most of these very inexpensive parts.

johnjh2o
Re: connecting plastic and metal plumbing

As stated by di1 replace the trap, including the chrome section coming from the wall. Use a plastic slip joint trap not a glue trap.

John

johnL
Re: connecting plastic and metal plumbing

How do you replace the chrome part? What's on the other end of it? How is it connected?

johnjh2o
Re: connecting plastic and metal plumbing

The way you describe it should be part of the old trap. If that is the case there should be a slip nut holding it in place. A picture would be a great help.

John

johnL
Re: connecting plastic and metal plumbing

Boy, this forum isn't very picture friendly! It keeps telling me my perfectly fine jpg file isn't valid.
Okay, Finally!
This is what I've got. You can see why I asked what's on the other end of the chrome piece.
Note that the wall is closed up nice and tight and freshly painted; that's why we had removed the cabinet, so we could re-do the walls. So I'm not really too eager to take the cabinet back out and re-open the wall.:(
By the way, I bought a straight piece to replace that bellows adapter and then found out last night that my new pipe has a larger diameter than the bellows so I just re-used it, in the mistaken belief that I would have the whole thing all finished last night.

Nestor
Re: connecting plastic and metal plumbing

JohnL:

You're not gonna like my advice, but I had the same drain piping as you in 21 bathrooms in my building. I found that the easiest way to prevent that lousy chrome plated drain piping from leaking was to replace it all. The problem is the stuff is thin as paper when it's new, and then it gets thinner as it corrodes in service. By the time it's 20 or 30 years old, any force you put on it to take it apart will put it out of round, and then it'll leak after that.

I'd:
a) remove the cabinet and wrap Saran wrap around those hot and cold Brasscraft stops to prevent plaster and dirt from getting into them.
b) you have a threaded brass collar soldered onto that chrome plated trap arm. They would have used a file to file off the chrome plating before soldering the trap arm into the threaded collar. If there's enough of the threaded brass collar sticking out of that 1 1/4 inch brass threaded elbow to grab onto with a pipe wrench, try unscrewing the threaded brass collar from the elbow. In my building, with 21 threaded collars screwed into 21 threaded elbows, not a single one came out with a pipe wrench. I had to replace the threaded elbows in all of them.
c) otherwise, you'll have to do what I had to do 21 times, and that is to cut the wall open and solder a new 1 1/4 inch threaded brass elbow onto your copper drain pipe.
d) the best way I know of to patch that hole then will be to use an angle drill to attach pieces of spruce 2X2 material to the closest studs and drywall screw a piece of drywall over the hole.

That looks like plaster walls, so you might want to shim out the 2X2's with anything that's 1/4 inch thick so that your drywall will be (close to) flush with the surrounding wall.

From what I can see, you'll also likely have to unsolder those brasscraft stops and solder them back on after you get the drywall patch up.

It's not an easy job, but it'll be much harder to do with the cabinet in place.

johnjh2o
Re: connecting plastic and metal plumbing
johnL wrote:

Boy, this forum isn't very picture friendly! It keeps telling me my perfectly fine jpg file isn't valid.
Okay, Finally!
This is what I've got. You can see why I asked what's on the other end of the chrome piece.
Note that the wall is closed up nice and tight and freshly painted; that's why we had removed the cabinet, so we could re-do the walls. So I'm not really too eager to take the cabinet back out and re-open the wall.:(
By the way, I bought a straight piece to replace that bellows adapter and then found out last night that my new pipe has a larger diameter than the bellows so I just re-used it, in the mistaken belief that I would have the whole thing all finished last night.

johnL All you have to do is loosen the lock before the chrome cover plate and the chrome part of the trap will pull out. Then you can replace the complete trap. Not just the bowl as you have done.

John

johnL
Re: connecting plastic and metal plumbing
johnjh2o wrote:

johnL All you have to do is loosen the lock before the chrome cover plate and the chrome part of the trap will pull out.

There isn't a lock on the cover plate, the only thing holding it there is caulk. It was just a chrome pipe sticking out of a real big hole in the wall. So we put a round piece of plastic to seal the hole, then caulked the chrome cover to it.

johnjh2o
Re: connecting plastic and metal plumbing

The correct way to make the repair is to open up the wall and remove the chrome pipe and extend the waste line behind it through the wall. The easy way but not the recommended is to cut the end of the chrome pipe off and and install this coupling. Then attach a new trap to the coupling. Also through that flexible extension tube out. All that will do is trap hair.

http://www.drillspot.com/products/371960/Fernco_PTC-150_Tubular_Pipe_Connector

John

Nestor
Re: connecting plastic and metal plumbing

JohnL:

I've seen those Fernco couplings used to replace chrome plated p-traps, and that's probably your best bet if you don't want to remove your cabinet.

But, all of those old chrome plated p-traps were a problem waiting to happen from the day they were made. That's because the metal that was chrome plated was brass, which is an alloy of copper and zinc, and zinc is a highly reactive metal.

If you've ever gone to change the rubber washer in an old water valve, you'll often find that the bibb screw is reddish brown in colour and crumbles under the force of your screw driver. That's because the head of the brass screw has been dezincified. The valve body itself is still strong because it's not made of brass, it's made of bronze, an alloy of copper and tin. Tin isn't nearly as reactive as zinc.

In a chrome plated brass p-trap, it'll be the brass below the water line in the trap that dezincifies the fastest and the soonest. Hopefully there's still some strength left in that trap arm since it was above the water line for most of it's life. But I'd be gentle tightening up the clamp that squeezes the Fernco onto the chrome plated brass. You don't want to crush that tubing.

And, if that doesn't work, then it's back to Plan A with removing the cabinet, opening up the wall and getting all of that chrome plated crap outta there.

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