My downspouts flow into drain that moves rainwater away from the house. I'd like to extend that drain further out. Existing pipe is Schedule40. There shouldn't be any loads going over the new section.

  1. Would DWV be appropriate? I had been advised to use Schedule40 but cost is much higher.
  2. How do you determine the thickness that is necessary? Should I keep at 4" or could I decrease it to say 2" or 3"? Not sure how to conceptualize this yet.
  • Any pipe you are comfortable standing on should be okay if not driving over it. I would stay at 4 inch, in case of heavy rain.
    – crip659
    Jan 26 at 19:50
  • 1
    What is "DWV"? Is that the same as thin wall? I always took Schedule 40 to be appropriate for DWV usage.
    – isherwood
    Jan 26 at 20:20
  • Is "DWV" the black corrugated landscape drainage piping? If not, please edit to clarify. I too, wouldn't go to a smaller size - in a heavy rain, it's entirely possible to back up a 2 or 3" pipe and the water will come out wherever there's a gap for it to do so.
    – FreeMan
    Jan 26 at 21:00
  • This is above ground, right?
    – popham
    Jan 26 at 21:03
  • I think of black ABS pipe for DWV. Unknown schedule but decent thickness.
    – crip659
    Jan 26 at 21:12

1 Answer 1


Neither Schedule 40 nor DWV rated pipe is required, in most instances, for gravity drainage of storm water. Thinner pipe with SDR ratings, commonly called "drain and sewer pipe", is perfectly suitable for that purpose. Pipe should never be reduced in size going downstream, as it facilitates blockages.

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