main drain line sizing?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by mporterf, Mar 20, 2008.

  1. mporterf

    mporterf New Member

    Mar 17, 2008
    I live in georgia and I am trying to plumb my own house, what is the min. size drain line under the house (crawl space). I know that from the house clean out to the septic tank should be 4", is the entire horizonal drain require to be 3" or 4"?
  2. Redwood

    Redwood Master Plumber

    Dec 15, 2007
    Service Plumber
    Either 3 or 4" is commonly used. Check with your local authorities.
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  4. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    It depends on your local regulations and the number of toilets in the house. Here if 3" is adequate it can run all the way to the septic tank.
  5. Herk

    Herk Plumber

    Oct 28, 2007
    S.E. Idaho
    Here, we're required to run 4" out under the footing, but other parts of the state have overlooked it and allowed 3" depending on toilets. 2 toilets = 3" required pipe size, and if one toilet is more than 15' horizontally from the others, 3" is allowed. But the pipe through the footing still has to be 4".

    Codes vary greatly on this, I'm sure. Personally, I'd want that third toilet to be piped into 4" even if I didn't have to, but I'm old-fashioned. :)
  6. BAPlumber

    BAPlumber Plumber

    Jul 18, 2007
    Journeyman Plumber, business owner
    Vashon, Washington
    What kind of house are we talking about. We could be looking at anywhere from a 3" building drain to 6" plus. Is this a 1 bath rambler or a 12 bath mansion.
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