Interesting that the later (and mandated) septic systems have a name:
enviroseptic. The early systems were anaerobic; meaning, they were sealed from the oxygen in the surrounding air. On the roof, small vent pipes keep pressures even.
These new ones appear to have large PVC "candy canes" to vent the system's contents.
Our neighbors' systems are "shared", and certain wind directions bring the odors to us.
Fortunately, the odors have been much reduced, although the reason is lost in time. It seems the problem was worse when new--ten years ago.
I'd suggest painting the "candy canes" in camouflage colors to reduce that visual reminder.
