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Thread: Venting Requirements - Basement Laundry tub pump

  1. #1
    DIY Junior Member
    Join Date
    Mar 2005

    Default Venting Requirements - Basement Laundry tub pump

    The washing machine was directed contected to the main drain just before
    exiting the house 6 feet above the floor of the basement. Installed a
    laundry tub and have the washing machine drain into that and installed a
    1/4 hp laundry tub pump to pump the waste water up to the drain. The
    laundry tub pump has it's own vent line which is not connected any
    exterior pipe and was left open and stops 6 inches above the laundry
    tub. There is an S-trap on the pipe from the pump to the main drain to
    prevent fumes from entering the basement.

    Problem is that the kitchen sink on the floor directly above the laundry
    tub how is be affected when the pump turns on in the basement. I hear
    sucking sounds like it is attempting to pull the water from the kitchen
    sink. Since this has started have had repeated problems with leaks
    under the sink. Have taken the sink drain apart and put it back
    together twice. It doesn't leak again until the using the washing
    machine several times. The vent line is 2", kitchen sink is 1 1/2"

    See attached diagram. Could the problem be that the vent for kitchen sink
    is clogged or ?
    Attached Images Attached Images  

  2. #2

    Default venting

    Since you titled your post to be about venting, here is a diagram with the laundry tub and pump basin vents done according to my local code requirements (IPC / IRC). Your code requirements may be different. Also important is to get a check valve installed in the pump discharge line. That s-trap is most likely not serving any pupose at all. The water in the verticle pump discharge will flow back down and fill up the basin some every time the pump stops running, most likely siphoning all the water out of the s-trap at the same time. Although the pump and your drians probably function fine as they are, you should get them vented to the outside air for health reasons if none other. That basin will not completely empty out and will hold some water, dirt, scum for mold and bacteria to grow in, and then be released through the open vent in your basement.

    As for the leaks under the kitchen sink.... are they leaking while the pump is running and the sink is not being used? or do they only show a leak when the sink faucet is running? Perhaps there is a partial blockage in the main drain line allowing the pump discharge to back up and leaking through faulty connections under the sink. No matter, the leaking connections under the sink need to be repaired or replaced as they should not leak for any reason.
    Attached Images Attached Images  

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
    Join Date
    Aug 2004
    Bothell, Washington
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    Very nice drawing Clayton.

    It does seem that his kitchen vent is too low, and not serving it's purpose.
    If it were plumbed like Clayton's drawing, and the vent relocated on the sink, it would be a going concern.

    The existing kitchen sink vent is lower than the p-trap.

  4. #4

    Default kitchen vent correction

    Here is an altered diagram with corrected kitchen sink vent options. On the second diagram I believe the UPC requires the trap closer to the vent than 5'.

    EDIT: changed the vent again on the first diagram.
    Attached Images Attached Images  
    Last edited by Clayton; 03-27-2005 at 08:22 AM.

  5. #5
    DIY Junior Member
    Join Date
    Mar 2005


    Thank you for your responses. Just bought this old house which was built in 1949 and will be remodeling the kitchen this summer and will address the laundry tub venting issues then. Good point on the wastewater in the tub. 98% of the water is from laundry only, so it is pretty clean, but it could produce problems. Since the only vent available is inside the kitchen wall, will have wait until summer to fix this.

    Regarding the kitchen sink, it leaks when running water into the sink. The leak is reoccurring in the S-trap. Have fixed it twice. The first time it was because of old rusty pipes which were replaced with PVC. That worked until doing multiple loads of laundry. Now it has a slow leak in the kitchen S-trap. Wondering if the sucking sounds that come from the kitchen sink when the pump is running could be causing the loosing of the connections?

  6. #6


    The sucking sounds are caused from venting issues or partially clogged drains and should not have anything to do with your leaks. You could have your vents and drains snaked in attempt to stop the sucking noises but that may not stop until the system is redone correctly. The leaks need to be repaired or replaced again. The only thing I can think of to contribute to the recurring drian leak is if the pump or something else is causing excessive vibrations through the drainage system.


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