I have not seen anything like that but that is not saying much LOL
Walk us through what this is...........the bigger pipe on the bottom is the ???
The pipe coming up and over pointed at the bottom pipe is ????
Haha. I haven't seen this before either. PB indicates it's standard. The top pipe is the backwash line from the DE filter.
The bottom pipe ties into the sewer line to run the backwash to waste.
The purpose of the air gap is two-fold. To prevent a sewer back up from getting back up the filter line and to prevent any kind of bacteria (or other nasties) from working its way back into the pool plumbing.