Importance of drop

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Giles, Sep 27, 2008.

  1. Giles

    Giles Retired tool & Die and Mechanic

    Joined:
    Aug 28, 2007
    Occupation:
    Retired
    Location:
    N.W. Alabama--Florence--
    I have a problem in an older basement home. The plumbing drain is sch.40 PVC. The kitchen sink and washing machine are on a 2" line about 60' from where they enter the main 4" line going down beneath the slab. I do not have a garbage disposel and all cooking and dinnerware utinsels are wiped out before washing. Very little food particles and cooking grease are carried to my septic system.
    I know and understand the importance of 1/4" drop per foot, but is it critical in my 2" drain situation? What is the minumum drop per foot for my 2" drain, considering the distance and the material that flows through it? It will be a major indertaking to correct this drain mistake. The amount of drop for the entire 60' is now 9". I have lived here for 3 years and I am just now encountering a drain problem.
    Basically, what I am asking is: Can I get by with less then 1/4" per foot drop with dirty water?
     
  2. Redwood

    Redwood Master Plumber

    Joined:
    Dec 15, 2007
    Occupation:
    Service Plumber
    Location:
    Connecticut
    The drain you have is about 1/8" per foot. While it may work the reliability will suffer and it is not to code for that reason.
    Plumbing to code is the best possible way to have plumbing that works!

    Is there a way to reroute this line to obtain proper pitch?
     
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  4. Giles

    Giles Retired tool & Die and Mechanic

    Joined:
    Aug 28, 2007
    Occupation:
    Retired
    Location:
    N.W. Alabama--Florence--
    I would have to drop the entrance point to the 4" main line the proper amount. This would result in a horizontal to vertical transition that would be below two full size baths. I dought this would be correct with any type fitting.
    I can only raise the drain at it origination point about 2", then it would be flush with bottom of floor joists. Strange, but understandable, that it took 3 or more years to present a problem. The proper plumbing, when the home was built, would have been to drop the toilet drains to allow for this long 2" run. As with a lot of rural homes, plumbing was not inspected.
     
  5. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    If the drain is not changed, then you may want to use something like Bio-Clean to keep the line clear of grease.
    I realize that you aren't "dumping" grease in the line, but there is some food matter or soap that is slowing things down.
     
  6. Redwood

    Redwood Master Plumber

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    Dec 15, 2007
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    Using Bio Clean on this line will definitely help.
     
  7. jimbo

    jimbo Plumber

    Joined:
    Aug 31, 2004
    Location:
    San Diego, CA
    I had a job once at a townhouse complex, where the 2" drain from the kitchen sink ran exposed in the garage straight across above the garage door opening....about 27' total, before turning straight down to the floor to enter the lateral. Although there was room to do that job right the first time, about half the homes had either zero slope on that horizontal run, or a belly due to poor support ( ABS pipe ) or both. The homes were in the neighborhood of 18 years old, and I think based on a long history of clog problems with that run, decided it was time to sell their stock in Drano and fix it!
     
  8. hj

    hj Moderator & Master Plumber Staff Member

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    drain

    It is not "strange" that it took 3 years to occur. What would be strange, now that it has happened once, is if it took 3 years to happen again. No matter how careful you are, unless you wash the dishes first and dump the water out the window, there will be grease, soap, and waste particles. Your drain does not have the adequate slope to create the self-scouring velocity needed to keep it clean as long as possible. Even with proper pitch it would eventually require cleaning.
     
  9. Redwood

    Redwood Master Plumber

    Joined:
    Dec 15, 2007
    Occupation:
    Service Plumber
    Location:
    Connecticut
    The only way you could come close to getting 3 years out of it again would be to have it jetted!
     
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