Live in lower level of a new condo. When my upstairs neighbor uses washing
machine, all of my drains gurgled. Called Plumber - He Snaked my toilet
and found that someone threw a pipe into a pipe across the street and it
was backing things up.
Now when my upstairs neighbor does washing only the front toilet gurgles
(and drains out water of toilet, sometimes bubbles in toilet). Plumber:
resnaked and no obstruction. Checked upstairs water connection - no
crossed pipes - all flow looked good, they gave me a new toilet in case
that was the problem.
And toilet still gurgles when upstairs neighbor does laundry.