I moved into my apartment a few months ago and I am seeing a lot of black small gnats or flies in the?

bathroom, my bedroom and sometimes in the kitchen. Then, I come home from work last night and in my tub around the drain I see something that looks like black tar. What is going on? Could the black flying bugs and the black "tar" be a sign of bad pipes. Is this something that can be fixed by my landlord or should I move. Looking forward to some helpful advice. Thank you!!