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Thread: Drain pipe size

  1. #1
    DIY Junior Member DMP's Avatar
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    Nov 2009

    Default Drain pipe size

    I am redoing my Master Bath. I removed the tub and shower and going to replace it with a two head shower, I was going to use the tub drain but it is only uses 1 “. If I use the shower drain that is 2” I need to move it 8’. (See Attachment)
    My question is having a vent that is 10’ from the drain will it cause problems with the p trap?
    Should I add the second 1 ” pipe (See Red dotted Line) just to make sure I do not have any problems?
    Thank you for your help
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    Last edited by DMP; 11-16-2009 at 09:37 PM.

  2. #2
    Homeowner geniescience's Avatar
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    Nov 2005
    humid summers hot, humid winters cold


    re-draw with lav drains, toilet drains and all venting. You will need a lot of help.

    in your next drawing, use one color to show pipes -- or two : existing, and projected. Don't use three different colors to show pipes.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    You cannot reduce the pipe size as you go down a drain, so the shower drain piping needs to be replaced to be 2" or more all the way to where it can drain into at least a 2" pipe. On a 2" pipe, the vent takeoff needs to be within (I think) 60", or 5' of the trap.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Aug 2004
    Cave Creek, Arizona

    Default drain

    What is a "safety pipe"? If you run the drain that far, regardless of 1 1/2" or 2", you need an intermediate vent. You are making the typical DIY mistake of assuming anyone can be a plumber as long as he can put some pipes together.

  5. #5
    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Jul 2009
    North Vancouver, BC
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    Default 1 1/2" vs 2" Pipe

    For a double headed shower system a 2" pipe is ideal.

    Your thoughts for the new vent line I agree with but at the same time that whole line should be changed to 2" not restricted to 1 1/2".

    You just can't snake out a shower drain line that is 1 1/2" very easily. A snake running down a 2" line goes like a hot knife through butter.

    You need to bust concrete anyway i'm guessing so bring the drain line up to 2" and the 10' distance is 2 far to wet vent it so the second vent line will be required by code.

    I'm not a plumber and every home has it's own chemistry. Re draw your sketch and there are solid guys here that can help you with the science side. My gut says this plan will work but I always bring my plumber in to give the final say. It never surprises me when I learn about a new code that I never heard of before - this is why it takes plumbers so long to get their ticket - there is so much to learn.

    Good Luck.

    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.


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