I hate cockroaches

Fuck, I detest roaches!!!  Ever since I moved into this apartment, I've always been careful not to leave at night anything that might attract any kind of bugs:  cockroaches, ants, etc.  I always wash all of my dishes, pots, etc., and wipe the cooking and eating surfaces.

Yet, lately almost everynight I'm finding small (upto 1/4 inch) cockroaches, which I always kill inmediately with some insecticide spray I have at hand.  Where did they come from?  When I do the cleaning of this apartment, I always finish it up by spraying the gap under the door so no bugs will come in the night from the corridor into my place.  Is it possible they're coming from the sewage pipes?  Yuck!!!

Good thing I'm moving out in a couple of days.