Anti-Siphon hole on sump/ejector pump discharge lines

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by michael-thomas, Nov 7, 2005.

  1. michael-thomas

    michael-thomas New Member

    Nov 5, 2005
    Occasionally I encounter a hole drilled in the discharge line of an ejector or sump pump a few inches above the pump and inside the pit.

    I’ve been told that this is an ant-siphon method (similar to the hole on a water heater’s dip tube) but I’ve not been able top find this documented anywhere.

    Can someone point me to a source such as manufacturer’s installation instructions or a code reference that describes when and how this should be done?


    Michael Thomas
    Paragon Home Inspection, LLC
  2. Lancaster

    Lancaster New Member

    Nov 7, 2005
    Quoting from Sta-Rite sewage pump installation instructions:

    "Drill a 3/16" (5mm) hole in the discharge pipe about 1–2"
    (25-51mm) above the pump discharge connection (but below
    check valve) to prevent airlocking the pump."
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  4. michael-thomas

    michael-thomas New Member

    Nov 5, 2005

    GOOGLE turned up this:

    "The vibrations and inability to pump on occasions can almost always be attributed to pump air-lock. When a sump pumps turns off, the water in the discharge line between the pump and the check valve drains back into the sump. If the pipe between the pump and the check valve is solid, the air in the line will compress the next time the pump tries to empty the sump basin. This compressed air can prevent water from leaving the pump. A 3/16 inch vent hole in the side of the discharge pipe inside the sump solves this problem. Check to see if your discharge line inside the pit has this hole. If it does, make sure it is not clogged.

  5. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    If the pump switch malfunctions and the pump removes all the water from the pit it will draw air into its volute. Without the hole to allow the air to escape as water reenters the pit, when the pump starts it would try to pump that air out first, but since it could not do it, the water would continue to rise in the pit until it overflowed, even though the pump was running. In addition, since the motor seal is water cooled and lubricated, running without liquid through the pump would damage the seal and allow water into the motor which would burn it out and require a pump replacement.
  6. sumppumppimp

    sumppumppimp New Member

    Sep 23, 2005
    This information is in all of the Zoeller Pump installation manuals! :cool: Zoeller recommends a 3/16" hole at or near the top of the pump but below the check valve.
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