Here’s a couple of pvc pipes in the front yard of a 4 year old home. The one on the left is clearly a sewer cleanout but the one on the right has me puzzled. It has a removable pvc grate on the top and 6" - 8" down inside is what appears to be an air-gap anti-siphon device but I can’t tell what it is connected to. There is no lawn sprinkler system. Any ideas?