How to find the other end of deck drains?

In our backyard lay a series of deck drains that perennially harbored standing water. Despite my best efforts, tracing the end of these drains proved to be an elusive task, seemingly due to the fact that it was compacted and buried beneath layers of earth.

I even ventured to employ a drain snake to address the issue, but the screws securing the drain covers were victims of rust, rendering them immovable.

Eventually, I noticed that one particular section near the periphery of our property boasted significantly lusher and denser grass. Upon closer inspection, I found the soil in this area to be moist. Spurred by this discovery, I began to dig around and, to my surprise, uncovered the elusive end of the deck drains. There was a flap that had been obstructed. Clearing the debris from the top of it led to an immediate release, and the deck drains finally emptied their standing water.