enter image description here

The problem is that this cast iron tee sticks out about .5" ahead of the studs. So this is preventing me from drywalling. The cast iron pipe at the bottom is flush with the studs.

So I am looking to replace this cast iron tee with a tee that would fit inside of the cast iron pipe because, if there was a tee that goes over the 2.5" pipe that would also prevent drywalling.

This cast iron tee connects a 2" steel pipe, 2.5" cast iron pipe, and 2" PVC pipe. It's for draining/gassing.

Labeled pic to make my problem more clear

enter image description here

Another zoomed out pic zoomed out

  • As a rule you want a drain from which watter comes to slide into a hole to which it flows. If you do it the oposite way you are increasing chances of things getting stucked on it. So no good options would go into the cast iron pipe. Instead look for something to go over it
    – Tomas
    Dec 6, 2022 at 6:48
  • Unfortunately the cast iron is flush with the stud, so putting something over it would prevent me from putting down drywall
    – byte
    Dec 6, 2022 at 6:53
  • 1
    I hope that stud through which the horizontal PVC runs is just decorative and isn't being counted on to support any weight.
    – FreeMan
    Dec 6, 2022 at 13:49
  • 4
    "cast iron tee sticks out about .5" ahead of the studs. So this is preventing me from drywalling." - that's the exact dimension of this not being a problem (notch the drywall) somewhere where a cabinet is going to hide it all anyway.
    – Mazura
    Dec 6, 2022 at 15:17
  • 1
    How did they do it before? What was covering the wall that was removed?
    – spuck
    Dec 6, 2022 at 20:00

7 Answers 7


Move (half) the wall, leave the pipes.

5/8" wood on the face of the studs, with 1/16" steel protective plates over the plastic pipe that's closer than 1.25" to the plane defined by the 5/8" as the new wall face. The cast iron should be adequately resistant to drilling to stop anyone who's not an idiot from drilling it.

Make the top of the offset in the wall face match the vanity or sink height if you don't want to move the upper half of the wall. Slap some molding on it and Make It A Feature. Good old wainscoting below the rail, even.

  • 5
    Sadly, they are making more and higher quality idiots all the time...
    – FreeMan
    Dec 6, 2022 at 13:57
  • Thanks this is what I ended up doing. I had not heard of wainscoting before, so that was extremely helpful to be able to visualize hiding the gap. Now to figure out how to nicely hide the gap....
    – byte
    Dec 9, 2022 at 3:56

You could replace the "T" with PVC that isn't as thick.

Or you could add firring strips to the studs and get the .5" clearance with a little extra.

  • 2
    Note that according to the picture, one corner of the PVC elbow is also an issue, so in addition to replacing the T you'd have to redo this to move it further back. If you don't absolutely need the space, I tend to agree that furring strips is the simplest fix. Maybe even consider building out just that bay; you'd have a step in the wallboard to deal with but that might not be hard to mask or make look deliberate.
    – keshlam
    Dec 6, 2022 at 5:44
  • Regarding furring strips -- I can not use them unless I rip out the drywall from ceiling to bottom. i.imgur.com/LmkcrfS.png This picture kinda shows you that this is the bottom half of the wall. Regarding the PVC T, unfortunately it would have to be tighter than the cast iron which is flush against the joint. Unless I can put in a T that goes "in" the cast iron pipe.
    – byte
    Dec 6, 2022 at 5:56
  • seeing the new pic, you will need to cut the cast iron above and below the "T" and plumb in all new PVC. If that drain is for a bath sink you can use 1 1/2" pvc.
    – RMDman
    Dec 6, 2022 at 6:09
  • It is indeed for a bath sink. How do I then plumb the 1 1/2" PVC to the cast iron?
    – byte
    Dec 6, 2022 at 6:33
  • 11
    +1 for furring out the wall. Heck, you could just put a double layer of drywall on this wall, cutting the inner layer around the pipes, then, with a bead of construction adhesive around the cuts, add a 2nd layer of drywall to the whole thing to cover the gaps. A metal protective plate across the massive wound in the stud for the horizontal pipe would both protect the pipe and help the stud.
    – FreeMan
    Dec 6, 2022 at 14:00

You can double up the drywall. The first layer is illustrated below and the second layer would go on top of it.

enter image description here

Re-working cast iron is just too big of a headache in my opinion. Preferably you would make a proper plan to rip it out entirely since you already have this wall exposed.

  • A) doubled layer of drywall is exactly what I was thinking, thanks for validating that thought. B) Cast iron is often praised for waste stacks because it's quiet - you don't hear water flowing through it from upstairs bathrooms as you might with PVC. Replacing it just because "it's cast iron" seems marginal.
    – FreeMan
    Dec 7, 2022 at 16:02
  • @FreeMan It has a service lifespan of 80-100 years so if it's approaching that age then this reno project is the perfect time to plan for replacement. Heck, replace with new cast iron; I never explicitly stated PVC =)
    – MonkeyZeus
    Dec 7, 2022 at 16:21
  • Fair enough. Might want to specify that in the answer itself, not everyone reads comments.
    – FreeMan
    Dec 8, 2022 at 13:31

I think MonkeyZeus is on the right track, but I have a simpler solution: 1x2 strips nailed to the studs on that side. Furring strips, as they are sometimes called, would work well here to push the wall in slightly so the drywall clears the pipes. Then you drywall over it. Trying to double-up drywall is a pain because you have to cut the base sheet first, then put another over top of it (and it's a good idea to glue them together). It's also far more expensive.

The only catch here might be that left side, where you don't have a full 2". Ripping one of these will be a pain, but you could possibly put up shorter rips staggered on that side. If you want some additional insurance, glue the strips to the 2x4.

  • "The left side" being the corner? One could leave the furring strip hanging in the air and just be sure to "know" to screw into the corner where there's stud behind to hold the screw/drywall. One potential drawback is that this could impinge on screw space for the side walls in the corner by effectively removing those 2x4 from the equation when looking for a place to attache the other wall. It may require a new 2x4 vertically in the side walls to support the drywall on each side of this alcove. Adding furring to the plumbed wall also requires furring out the top & bottom plates.
    – FreeMan
    Dec 7, 2022 at 16:07

You need to first know what you are doing because the materials are wrong. Sanitary drainage fitting’s are needed, not pressure fittings. Cut the cast iron hub and use a rubber gasket with a sanitary tee (2x2x1 1/2). Also use a 1.5 inch bend with a trap adapter and you’re done. As for the stud, reinforce and use a hole saw.

Florida Master Plumber Contractor Nick


I'd cut the metal off horizontally inline with the upper horizontal pvc pipe and I'd cut the cast iron off leaving enough room at the bottom for a fernco to transition back up to the pvc.

Before removing the support for the upper metal pipe I'd get some metal pipe strap and securely wrap it around the pipe and secure it into the side studs. Once you cut away the support this pipe can want to fall downwards. This is a much bigger concern with cast but you still don't want your metal vent pipe pulling out of the roof flashing.

I'd put a 2" fernco metal to 2" pvc coupling from the metal to a new 2" pvc sanitary wye.

On the bottom leg of the new pvc why I'd use a 2" no hub fernco to go from cast to the pvc.

You can get no-hub rubber couplings in pretty much any diameters.


image from jay613

  • Thank you for your explanation! Is there a male adapter where the coupling would go on the inside of the cast iron pipe? I’m afraid I don’t have any clearance to add any thickness to the cast iron pipe.
    – byte
    Dec 6, 2022 at 7:24
  • 1
    Some of these couplings are little more than a rubber sock and a metal band maybe 1/8" thick. Also if you are putting this coupling at the floor level then you can trim the backside of the drywall or avoid the drywall around it and just tape across it and mud it or hide it with the baseboard. Dec 6, 2022 at 7:50
  • I think my answer is similar or identical to this one ... is that right? If so I'll delete mine. You can take the crude drawing if you want. :)
    – jay613
    Dec 7, 2022 at 16:57

This option is bit more involved, and working with pictures makes this hard to determine if it is actually a possible solution. But options and thoughts never hurt. From picture 2, it seems as though the PVC on the smaller side of the tee may be intruding on the drywall space as well? If So a PVC Tee will probably not solve your problem.

I'm not a residential plumber, so I can't comment on the design of the drain. However, if this was my problem to fix I would consider cutting the surrounding galvanized and cast piping to make room for a die-electric fitting or most likely enough brass to braze a copper Tee in line. Copper will give you the most clearance without sacrificing pipe diameter.

That said, galvanized steel must have the zinc coating removed, so if that is a Sch 10 (super thin) pipe, you may not be able to get it clean enough. If you can remove it, maybe you can get it threaded with a coupling to a threaded brass nipple with the threads cut off the other end.

Warning: If you are considering this way please make sure to do your research on copper/steel electrolysis, and galvanized vapors.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.