I noticed a few weeks ago during the rainy season that underground drainage from my downspout was flooded and not draining right. I purchased a pressure washer attachment that promised to unclog things like this and went to town.
I could hear it underground and after being stuck at the same distance for a while I decided to start digging at that spot. I found a elbow pointing up and a green attachment. My guess is it's supposed to be above ground, and just got buried from years of neglect; I didn't know it and have owned the house for several years.
What is the correct way to reinstall this so it drains properly?
Running a pressure washer attachment through the drain:
After about 20 minutes of trying to snake it around a corner I decided to dig and found this:
The device attached the PVC elbow appears to pop up as needed: