i have the same problem,,,

only its coming from the owner's closet floor drain which also serves 4 floors of wtr htrs above us,,, 1 of these days i'll have to hammer out the conc & replace a broken cast iron trap,,, til then, i caulk'd a plastic baggie over it so the renters won't disturb their vacations,,, when poss, i run some chlorox into the trap & that works for a couple days,,, my quik-fix won't work for you, tho.

in theory, there's no difference 'tween theory & practice,,, in practice, there is !