Flies in the bathroom..

Ive just discovered flies breeding in my bathroom. at the moment only 1 or 2 appear at a time. What should i do before they zerg rush my apartment?

I just came back from battle, I equipped my gloves, cleaning brush, and cleaning spray, turned on some battle theme music and went in to clean the fuck out of my shower. Then i poured drano down all the sinks. That should kill them all off.