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  1. #1
    Join Date
    Jun 2012
    Posts
    81

    Default addition with a full bath?

    i am in the process of building an addition that will have a full bath in it. i am close to doing the ground work for the bathroom (slab on grade addition) and have conflicting advise on the size of the waste line to the septic. i have been told to use 4" line by some and 3" line from others. i will be tying into the existing line to the septic tank with a vertical drop hook up. i thought 4" would leave too much open pipe and therefore increase the risk of liquid out running solids and that the 3" would drain better with less risks??

  2. #2
    Join Date
    Feb 2010
    Location
    South*East
    Posts
    1,217

    Default Re: addition with a full bath?

    Three inch is more then large enough inside the addition but it should be increased to four were it exits the building.

    John

  3. #3
    Join Date
    Jun 2012
    Posts
    81

    Default Re: addition with a full bath?

    ok- so the 30' inside (under slab) should be 3" then when it passes the foundation transition to 4" for the remainder? why would it need to increase outside? the 3" pipe and fittings will definitely save money as compare to the 4".....thanks

  4. #4
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: addition with a full bath?

    The slope inside is greater, and thus the risk of 3" clogging is far lower than the flatter pipes outside the house in the septic system.

  5. #5
    Join Date
    Jun 2012
    Posts
    81

    Default Re: addition with a full bath?

    that makes sense to me except the inside slope is greater part..... 1/4" to a foot slope for the entire pipe run untill the vertical drop tie in......

  6. #6
    Join Date
    Jan 2008
    Posts
    2,188

    Default Re: addition with a full bath?

    Cost matters but more important is a trouble-free future. I'd run 4" for the whole thing because the larger pipe is less likely to clog. Since this is sub-grade be sure you've got a good clean-out planned here. That's another reason I'd go with 4"; the radii are longer so cleaning out will be easier if it's ever needed. Just my opinion-YMMV

    Phil

  7. #7
    Join Date
    Dec 2010
    Location
    Houston Texas
    Posts
    2,969

    Default Re: addition with a full bath?

    Pipes in a septic field are level. The pipes inside the house are not.

  8. #8
    Join Date
    Jun 2012
    Posts
    81

    Default Re: addition with a full bath?

    ok, i understd a litlle clearer now. spoke with my plumbing inspector and he suggested running all main line at 3" inside and outside of the structure. he spoke of 3" flowing solids more favorably over the 4" for a 1 bathroom line.......
    i asked about running 3" inside the structure and transitioning into 4" after it leaves the foundation and into the main line tie in into the septic tank.

    as i understand your coments about all septic lines are level..... this would be in regards to lines AFTER the tank correct? my work is all BEFORE the tank. thanks.... thoughts??

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