Strange kitchen sink backup problem

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Tommy, Feb 13, 2021.

  1. Tommy

    Tommy New Member

    Joined:
    Feb 13, 2021
    Location:
    Northbrook, IL
    Hi All,

    Have a strange problem at my parents home. Their laundry room is in their basement. Also in their basement is a sewage ejector pit. The laundry room sink drains down into the basement slab, so I assume it goes to the ejector pit as the main sewer line right next to the ejector pit is higher then the laundry sink drain.

    Yesterday I was running the laundry sink on full blast for about 10 mins and all of a sudden the kitchen sink which is on the second floor above the basement started backing up. It's a double sink and the side of the sink with the garbage disposal started backing up dirty water. After the laundry sink was shut off, the water went down and the kitchen sink seemed to be draining fine.

    The strange part is, when the kitchen backup occurred while I was running the laundry sink, the laundry sink wasn't backing up at all. Water was going down the drain with no issue. I went upstairs and ran the kitchen sink to try and figure out if it was somehow connected to the laundry room sink, which would mean it's also going to the ejector pit. I confirmed that wasn't the case as I could hear the water drain directly into the main sewer line.

    I noticed there is another PVC pipe coming downstairs into the laundry room which also connects to the drain line where the laundry sink is also draining... I'm assuming it's a vent pipe but I couldn't confirm. At first I thought it was somehow connected with the kitchen drain.. but when I heard the kitchen sink draining to the sewer line on the other side of the basement I ruled that out.

    As I mentioned, I'm pretty sure the laundry sink drains to the ejector pit given it goes into the slab. So I'm completely confused how the laundry sink can cause a backup in the kitchen above - and with no water backing up in the laundry sink! :confused:

    Any thoughts on what could be happening here and what I should do next? Thanks in advance.

    -Tommy
     
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    A sewage ejector will pump to a 3" or 4" line that is drained by gravity. Since the laundry tray in the basement is going to sewage pit, that water is then pumped uphill to the gravity line. The kitchen sink on the next floor also drains to that gravity line, meaning, that somewhere a drain needs cleaning.

    Now if the sewage ejector is pumping to the 2" kitchen line instead, that's not going to take much water and it may cause the water to rise up to the sink. Not only is the kitchen line too small to drain that way, but over time the grease buildup can reduce it further.
     
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  4. Tommy

    Tommy New Member

    Joined:
    Feb 13, 2021
    Location:
    Northbrook, IL
    Hi Terry,

    Yes I can see ejector discharge line which goes up and then down right to sewer main a few feet away. So if I'm understanding correctly, you're saying the issue may be instead of the waste going through the gravity line and into the main sewer line, there is a blockage between the ejector discharge line and the main sewer line which is causing the pumped out waste to be diverted upward into the system which then causes the water to come out in the kitchen sink?
     
  5. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    The pumped line must be able to freely push water through into a clear 3" or 4" line. Inspectors in Seattle like to see it dump into a 4" line.
    Anything restricting that flow is going to back things up.

    [​IMG]
     
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  6. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    He is saying that.
     
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  7. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    usually a pumped waste dumps into a 4 inch maybe a 3 inch but a 2 inch wouldn't be right. the good news is your pump works good but you need to verify where discharge goes and size of pipe . you might need to run a snake down the gravity drain
     
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