I live in New England and have been experiencing unprecedented basement flooding in the past 1.5 years… our basement is unfinished and it has been recommended that I install 2-3 more sump pits and pumps in the basement to control the high water table and mitigate flooding.

Given the layout and grade of our yard, I’m going to drain all of them to one far corner of the backyard where I’ve already installed a dry well.

Each sump pit would have one primary pump. But after the check valve on each individual pump’s discharge line, could I connect all of the pumps to one common discharge line/pipe in the basement before directing it outside? Thanks

  • Would it be possible to let gravity take over at some point? It would be better if possible to use an unpumped common pipe after an air gap so the pumps can't push water at each other. Eg run the pumped lines a couple feet above ground then run a large common pipe along a wall or hide it in rocks.
    – jay613
    Commented Mar 11 at 7:05
  • Thank you. that is a really good point. I had thought that I could possibly have the static head high enough on each individual pump’s discharge that gravity could feed them together into a common pipe inside the basement before sending them outside on the same line. But maybe I’ll just feed them out individually and run the common pipe along the outside of the house. I was avoiding the latter because we have a shallow corrugated downspout drainage pipe right where I would want the coming sump discharge pipe to be… so it could end up being kind of an eyesore along the ground surface.
    – Pommeblanc
    Commented Mar 12 at 0:43

1 Answer 1


You could... if you up-sized the pipe they are joining into. You do not want to have any back pressure on a sump pump. If your pumps are all 1" discharge then run a 2" trunk line that for them to tie into.

  • This is great—thank you for your help. Do you think a 2” trunk line diameter would suffice if the pumps are all 1.5” discharge? Or should I up-size the pipe even more?
    – Pommeblanc
    Commented Mar 12 at 0:32
  • Basic math suggests that three 1.5" pipes need a bit more than 2.5" pipe to take the combined flow, so 3" would be the available choice. That will also take a fourth pump, just. Word of advice - provide a vent (even an AAV, if a regular vent is too much trouble) on the shared line, or you can have flapping on your check valves.
    – Ecnerwal
    Commented Mar 12 at 18:48
  • Thanks—I’ll upsize to a 3” and vent for sure. I appreciate it.
    – Pommeblanc
    Commented Mar 15 at 11:53
  • A bit late, but I'd also suggest putting a secondary check valve on each individual output line, in case the internal check valve of the pump fails. You do NOT want a check valve failure to result in one pump pumping into another pit rather than outside. "Speaking for a friend..."
    – Milwrdfan
    Commented Apr 10 at 14:34

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