Today, I hooked up the downspout to the drainage pipe:

The “tightline” connection to the downspout is now complete.

Now we’ll see what happens at the bottom when it rains. I still want to make the pipe end in a “dry well” gravel pit (maybe a good use for all the rocks I’ve dug up) and maybe make a drain hole in the lava wall at the bottom of the lawn so the water doesn’t flood the lawn. But that’s all extra credit. First the perforated pipe needs to get laid down.