Waste Line Slope to Septic

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by bdey01, Jun 10, 2014.

  1. bdey01

    bdey01 New Member

    Jun 10, 2014
    I am having a new septic tank and drain field installed at my home for a renovation/addition, and everything is going smooth, but the septic guy, who is well known and very praised for his quality of work in the area, swears that the proper slope to install the line running from the house exit to the tank at a slope of 1" per 10 feet, which works out to just over 0.8%. It is a 3" line, so I thought that the line needed to be sloped no less than 1%, which would be 1.2" per 10 feet. I am not wanting to questiong his experience and make him mad, and no one else is questioning it, like the inspector, so I am a little at a loss. He has been in the business for over 35 years, and his explanation is that the shallower slope allows for the solids to stay with the liquids better but still keep moving downhill, whereas the 1 and 2% slopes that others use are too frequently causing the liquid to outrun the solids, causing clogs. He does acknowledge the 1% slope, so I am not sure if he is on the level with this (pun intended). Any advice before they bury the pipe today?

  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    That's a new one.
    My plumbing code like a 2% or 1/4" per foot.
    2-1/2" in ten feet.

    For a 4" line, an inspector can okay 1%

    At least he's not running it flat.
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