I am reconfiguring some of my water drainage, and wondering how to make some of the connections in the pipes that will share the same ditch.

My plan is to run 4" corrugated perf pipe at the bottom of the ditch for the french drain system, along the side of my house, all the way to the back of my yard where everything slopes down to. I'll put a pop-up emitter on the 4" pipe at the end. But then about half-way down the length of the ditch, I want lay in some 3" corrugated solid pipe to carry the water out from the downspouts, and that pipe will go to its own pop-up emitter. I also have a sump pump discharge, which is 1 1/2" PVC pipe. Here's the thing, I would like to run that to a wye fitting into the 3" corrugated pipe that is carrying the downspout water. So, how can I connect up the pump discharge into the 3" corrugated pipe? I can't find any wye fittings that will accomplish this directly. They do make 3" corrugated wye fittings, and I was thinking I could adapt the PVC pipe to 3" corrugated, and then in the 3" corrugated wye. But I can't find adapters that have 1 1/2" PVC on one end, and a 3" snap-on coupling for the corrugated pipe on the other end.

This is solid pipe, and I don't want it to leak. So, is there an official way I should be doing this, or do I have to MacGyver something?

  • Other than "they are both pipes, right?" These are pipes with totally different purposes and thus totally different families of fittings. Grab some chewing gum and get to MacGyvering. Or pick compatible types of pipe.
    – Ecnerwal
    Jan 4 at 2:04
  • But it's not up to me. The downspout cleanout/vent assembly discharges into 3" corrugated, and the sump pump discharges into 1 1/2" PVC. I can't be the first person in the world that needs to drain both of them to daylight. Why would that be a totally different purpose? Jan 4 at 2:30
  • I'm not seeing the problem. There are products for this purpose. You may need to use reducers if you're mixing and matching various pipe sizes. homedepot.com/p/…
    – Huesmann
    Jan 4 at 14:19
  • Please give Angus' name proper capitalization... :)
    – FreeMan
    Jan 4 at 16:15

1 Answer 1


In the highly unlikely event that your 1-1/2" PVC pipe is not schedule 40 pressure pipe, but SDR, a 1-1/2" to 3" SDR reducer/increaser is a thing, and 3" SDR to 3" corrugated is a thing, though if you think corrugated fittings are leakproof, think again. Corrugated is strictly drainage tubing with snap together joints and has a much lower standard for "tight joints" than glued PVC, whether SDR or schedule 40.

In the more likely event that the 1-1/2" pipe is schedule 40, The most likely combination would be 1-1/2 to 3" schedule 40 and then a 3" schedule 40 to SDR coupling, then the SDR to corrugated fitting. I've never seen (might be orderable?) a 1-1/2" schedule 40 to SDR fitting. 3" and 4" they are commonly available.

  • Thanks for the suggestion, I'll look for those parts, it is definitely schedule 40 pipe. It's not a big issue if water leaks, but I want to prevent any future root intrusion. I intend to use this mastic tape that is designed to keep drain pipe connections from leaking: frenchdrainman.com/product/4-x-108-fdms-200-year-tape Jan 4 at 20:56

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