Ari, I get the same problem at home. One or two every now end then. What I do is spray Baygon (or similar brand) down the drain and this stops them for a month or so. Unfortunately, if you do not fumigate the communal spaces (stairway, entrance, boiler room) they will keep appearing (you only need to fumigate once a year, but then you cannot use water for 72 hours, so unless you are away from the house for a long weekend, it is a waste of money) . They seem to multiply in the sewers and when they find an opening they surface and become a nuisance.