How to connect downspouts to underground PVC drainage
By My Yard Editorial Team · 7/28/2026
The Quick Answer
Use 4-inch solid SDR-35 PVC with a 1–2% slope and a cleanout at every downspout connection. Expect $12–$25 per linear foot if you hire it out.
The Witty Breakdown
Corrugated flex pipe is cheaper and it's why so many buried systems clog. The ridges catch grit and roots find it charming.
Every roof surface generates about 600 gallons per inch of rain per 1,000 sq ft. That's a lot of water to aim carelessly.
Step-by-Step Fix
- 1
Use solid smooth-wall pipe, glued fittings, no flex.
- 2
Add a cleanout riser at each downspout and every direction change.
- 3
Maintain a minimum 1% continuous slope to daylight.
- 4
Finish with a pop-up emitter or daylight outlet well away from the house.
Pro-Tip / Do Not Do This
Never tie roof drains into a footing drain or sump. You'll overwhelm the system exactly when it matters most.
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