When my washer drains, the water flows into my septic tank. Immediately, septic odor comes from the septic tank area outside (not from the washer, not inside the house). I suspect that the volume of water is displacing some stinky gas and it is not escaping where it should. Where should that gas escape?

I don't notice it when I use other drains, but it might be just the massive volume of water that makes it noticeable from the washing machine.

Thanks

You don't need me my friend. You did a great job of analyzing the problem yourself. That's exactly what's going down. Is there a vent on your septic tank? Cheers, Tom