My downstars toilet is gurgling when I flush up upstairs toilet. I just snaked the downstairs toilet with a commercial electrical snake 2 weeks ago and it seemed to have fixed the issue. Now I am having the same issue along with a foul odor in my basement. The odor is especially bad when I do my laundry.

Get the sewer machine back and snake the roof vent. Put out enough snake to reach the base and 20 feet more. Good luck, Tom