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Thread: Size of drain pipe for toilet and sink

  1. #1

    Default Size of drain pipe for toilet and sink

    What is the "standard" size for a drain pipe for a toilet and for a sink? I am considering finishing out my walk-up attic and thinking about putting a bathroom in it. When I had the house built, I had the builder run 3 3" PVC (schedule 40) pipes from the basement to the attic. At the time, I was thinking that I might use them for electrical chases but now I'm wondering if I can use one of them for a drain pipe for a bathroom in the attic. My first question is whether 3" pipe would be sufficient for a toilet dran and a sink drain. My second question is whether I can use one 3" pipe for both the toilet and the sink.

    A related question (which might have to go in the electrical code forum) is whether I can use one of the pvc pipes as a chase to run NM wire and telephone and data cable (from the basement to the attic). Of course, I would only be able to secure the cable at the entrance and exit of the chase and couldn't secure it while it is in the chase.


  2. Default

    A 3" pvc pipe is find for a tolet and sink and anything else you will likely be installing. I expect that you will research your venting requriements for those fiztures. Also, it would be nice if you could check with your builder to make sure that those 3" runs were cemented together. I don't think you should have trouble running your wires in the same pipe, but you might want to post that int he electrical forum. Good luck.

  3. #3
    Join Date
    Oct 2003
    Living in, not from North Carolina


    3" pipe is fine to run the toilet and the vanity water in, you can run both in one pipe. (check the venting before closing up the wall).
    Finnegan has a good point as well, make sure the builder glued the pipes together after all if you told him they would be used as chases for electrical, there would have been no need for them to be glued.
    Running electrical cable and data cable in the third 3" pipe is also fine.
    Last edited by pushkins; August 11th, 2011 at 05:21 AM.

  4. #4
    Join Date
    Dec 2003
    Welland Ontario


    Phone and power cable can not be run in the same chase unless the phone cable has the same voltage rating as the power cable on the insulation.

  5. #5


    Thanks for the replies. I'm sure the builder won't know if his plumbing sub glued the pipes together or not so the best way I can think of to "test" whether thay are glued or not is to locate a few joints and see if there is any purple primer around them and whether I can pull them apart (my theory being that if one or two joints are glued, the rest are also). Even if I do that, I'll have to think about whether I'm willing to take the risk that they are all glued. I think the plumbing subcontractor installed the chase so I may call him and ask him if he remembers whether he glued them or not.

    Venting shouldn't be a problem since this is an attic. I can easily vent everything out through the roof.

    As to using the remaining chase for the electrical/phone/data/cable and the requirement that all wires must be the same voltage, I'll have to check that out. If I can't use use one chase for electrical/phone/data/cable wire, then that means I'll have to split the wiring into 2 chases and probably skip my plans for adding a bathroom since I wouldn't have a drain pipe to use. I'll post my question in the electrical forum and check with the local electrical inspector (he's great to work with).

  6. #6
    Join Date
    Dec 2003
    Kent, WA


    Since your pipes are so huge, I believe you can combine LV and 120/240VAC wires if you install a smaller raceway in that 3" pipe. Use a flexible plastic raceway (like ENT), perhaps in 1" size and run the smaller of the HV or LV bundle in that separate raceway.
    Kent, WA

  7. #7
    Join Date
    Mar 2006
    Kea'au, Hawaii

    Default Data Cable + Power in same Raceway ?

    Coming from an industrial process controls electric background, you may not want to run communications lines next to power lines. Long parallel runs tend to induce 60 cycle hum into them. Best to keep them seperate by several inches, or shield them from EFM pickup.

    Will post again on the electric side of the forum.

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