SEPTIC TANK INSTALLATION DEPTH

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Jazzman, Mar 13, 2020.

  1. Jazzman

    Jazzman Member

    Joined:
    Oct 14, 2015
    Location:
    Oregon City
    Hi, I’m replacing old metal septic tank with new code-approved norwesco low profile 1,000 gallon tank in Oregon. I can’t seem to find info I amount of cover required. The digging is really difficult in my area so I don’t want to over dig. You can get a riser as small 6” high. Would that be adequate and set outlet deep enough underground. I can adjust inlet from house to get required 1/4” per foot drop.

    Thanks!
     
  2. hj

    hj Moderator & Master Plumber Staff Member

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    You run the pipe from the house and set the tank so the pipe goes INTO its opening. THAT will determine the depth of the tank.
     
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  4. Jazzman

    Jazzman Member

    Joined:
    Oct 14, 2015
    Location:
    Oregon City
    Ok, thanks.
     
  5. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    I was thinking somebody would comment on the minimum depth for the building sewer pipe that goes to the septic tank.
     
  6. LLigetfa

    LLigetfa DIYer, not in the trades

    Joined:
    Feb 6, 2011
    Occupation:
    Semi-Retired
    Location:
    NW Ontario, Canada
    That would most likely be grandfathered in. Unless there is a pump, everything relies on gravity and pitch.
     
  7. Jazzman

    Jazzman Member

    Joined:
    Oct 14, 2015
    Location:
    Oregon City
    I looked up the installation instructions on the Norwesco website and it stated “excavate to a depth that will provide a minimum of 6” and a maximum of 36” cover over the top of the tank”
     
  8. Smooky

    Smooky In the Trades

    Joined:
    Apr 4, 2011
    Location:
    North Carolina
    Here in NC the tank depth is determined by maximum trench depth for a gravity system. Soil conditions, how deep rock is located or water table depth determines trench depth. In some cases the trench depth is very shallow in wet areas or in some cases in a mound. The plumbing has to be held high or a pump tank and pump will be needed. . . . With an existing system you will have to match it up to what is already there if you are keeping the existing drain field.
     
  9. LLigetfa

    LLigetfa DIYer, not in the trades

    Joined:
    Feb 6, 2011
    Occupation:
    Semi-Retired
    Location:
    NW Ontario, Canada
    Code here for the field pipe leach bed dictates everything upstream of it. We are allowed to only dig down 2 feet into existing soil. Then there is 3 feet of base, then the field pipe and another 18 inches of cover. Many rural homes here sit up on a mound and have another very prominent mound that is their leach field.

    I wanted the leach bed to be as low as possible and also wanted the first floor of the house to be as low as possible and not have to use a sewage pump, so I put in the leach bed and septic tank before excavating for the house foundation.

    From the distribution header to the septic tank, I calculated the minimum pitch to set the tank depth. From the inlet side, I calculated the required pitch for the pipe to the house which determined the elevation for the first floor.
     
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