If its a new apartment, Could be grout in the floor waste. Tilers are lazy bastards and wash their grout down the floor waste. You end up with a rough surface that bacteria can grow on. Break up the grout and flush it out. Drop some chlorine in the pipe and that should fix it
DISCLAIMER
All advice is given with-out seeing the job, and hence all advice MUST be taken as advice with limited knowledge on the exact situation. NO responsibility can or will be taken. And yes, I am a licensed Plumber and Drainer with my own business in Brisbane Australia.
