How do you connect a gutter downspout to PVC pipe with an adapter?

Match the sizes

• A 2 by 3 inch downspout usually pairs with a 3 inch round adapter and pipe.
• A 3 by 4 inch downspout usually pairs with a 4 inch round adapter and pipe.
• The downspout should drop into the adapter, so water flows from the upper piece into the lower one and cannot leak out at the joint.

Choose the right pipe

Smooth-wall PVC drain pipe is easier to clear and less likely to trap debris than corrugated tubing, whose ridges catch grit and granules. Use solid, not perforated, pipe to carry roof water away. Perforated pipe leaks water along the way, which defeats the purpose near a foundation.

Slope and outlet

Keep a steady fall the whole way, commonly at least 1/8 inch per foot and more where you can, with no low spots where water and silt sit. End the line where it can drain freely: out to daylight on a slope, or at a pop-up emitter in the lawn. Georgia clay absorbs water slowly, so pop-up emitters on flat clay can back up in a long storm. Where soils are known to be expansive, the residential code calls for roof water to be discharged at least 5 feet from foundation walls.

Mistakes to avoid

• Tying downspouts into the foundation footing drain, which floods the drain that is meant to keep the foundation dry.
• Connecting to a sanitary sewer, which local rules generally prohibit.
• Burying a line with no way to clean it. A cleanout or a removable strainer at the top saves digging later.

Keeping debris out of the gutters keeps it out of the pipe too. See gutter sizing, seamless gutters and guards and the Georgia roof maintenance checklist.