I'm installing a 4" corrugated/perforated plastic pipe into a drainage ditch (2-3ft deep "French drain") in my yard uphill from my house (which sits on a steep [wet] slope). There is already a 12" pipe (perhaps plastic/corrugated) buried in the ground along the property edge running perpendicular to the location I want to put the 4" pipe. I would like the 4" pipe to drain into the 12" pipe. What is the appropriate way to do so?
Some ideas:
Drill a hole into the sidewall of the 12" and allow 4" to fit horizontally into drilled hole so that 4" pipe drains into 12" pipe.
variation of #1 but with intentional "y" angle to allow incoming water to enter 12" pipe from uphill-to-downhill angle.
Bring 4" pipe over 12" pipe and connect from above (drill 4" hole into top of 12" pipe and let 4" pipe/connector extend vertically downward into 12" pipe
or is a coupling necessary? T or y? (can I get a mixed-diameter coupling with mixed 12" and 4" ends??
Any suggestions?