I live in the ground floor flat of a converted Victorian House and have recently come across a rogue pipe that shoots water out sporadically into an external drain kind of like a toilet flush swoosh sound, but the water is clean. I have no idea where this is from or what it could be - Can anyone shed some light? It is a white plastic pipe that comes from under the house (there is a basement, but it is tanked). I initially thought that it was noise from an upstairs toilet of a flat above, but saw it pump out with my own eyes today ( and subsequently make the drain at the side of the house overflow!) I hope someone can help - thanks

  • Size of the pipe? And is the water really clean, or just clean-ish? (maybe soapy?)
    – brhans
    Mar 16, 2016 at 21:08
  • 2
    Can you add a picture? It sounds like it might be a sump pump, as that's the typical "pumps out the side of the house" scenario, though that water is typically somewhat dirty. How does it make a drain overflow? Mar 16, 2016 at 21:14
  • Also what does a "tanked" basement mean? Mar 16, 2016 at 21:14
  • 2
    Could it be discharge from a sump pump?
    – Tester101
    Mar 16, 2016 at 21:15
  • Sump pump or water softener discharge? Mar 16, 2016 at 21:54

2 Answers 2


If this pipe is just above ground level and is spewing clean water out onto the ground (or is otherwise unchecked), it is more than likely coming from a sump. This sump could be from a drain tile or the A/C drain. If you have access to the basement, this can easily be determined by tracing the pipe back from where it goes through the wall/structure, unless it is all behind sheetrock.

(NOTE: I didn't see Tester101 and Fiasco Labs comments prior to writing this. I'm basically agreeing with them.)

  • Hmm yeah I like these ideas too. It appears it could be any or all of the above.
    – ArchonOSX
    Mar 17, 2016 at 10:50

Recently, plumbing codes have begun to require "trap primers" or an extra deep trap for floor drains to keep their traps full of water.

I would propose that is what you have here. To keep the external drain's trap filled with water the trap primer is occasionally pumping water into the drain.


More common is a primer that is connected to the potable water supply and activates when pressure fluctuations are sensed, such as the flushing of a nearby water closet.

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