I live in a typical suburban home. My sump pump discharges water up from the beneath the slab about 9 feet and moves outside through the rim joist. The pipe then turns into the ground and joins the downspout drain line out to the street.

Do I need to worry about water siphoning back into the basement after a pump cycle during a flood event where the street is filled with water, over the drain line exit?

1 Answer 1


The output pipe should contain a one-way valve not far from the pump. Otherwise, your 9 foot column of water would drain back into the sump bucket when the pump shuts off. This also prevents any siphoning when the pump isn't running.

  • Are any check valves truly 100% water tight?
    – Evil Elf
    Commented Jul 3, 2018 at 0:42
  • @EvilElf, they're designed to be water-tight. There is also the weight of the 9 foot column of water pushing it closed.
    – fixer1234
    Commented Jul 3, 2018 at 0:44
  • The weight of the water column is a good point.
    – Evil Elf
    Commented Jul 3, 2018 at 0:45

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