5 months ago I re do my drain field and snake the trap on the roof, now I'm getting a foul odor from the bathroom drain, and it was the same drain that started to back up when I first started to have trouble with my septic tank. So what is causing that? bad smell only in that bathroom drain and how to I get rid off that smell?

Make sure you don't have a cracked trap that is leaking water and draining out.

When you flush or drain is there any bubbles or gurgles in any bathroom fixtures? Back to you, Tom