My house was built in 2009, has a septic system, and since new there has been a septic smell from the vent pipes on very still days. Strong enough that you don`t want to be outside. Filters helped but now we are getting a very strong septic stench in the laundry room only when the washer is draining as if the gas is coming up the p trap when the water rushes by. The washer is a front load LG and I know they have had smell issues but this is definitely septic, not mold or gunk. I know the vent pipe smell may be unavoidable but the washer smell should be. Attached is a pic of the washer plumbing. It passed inspection but does everything look right? Could the septic system have been installed incorrectly allowing the gas up the pipe? Any other ideas? thanks!