How do you say "Clean" as in "clean a city" How would one say "clean" as in "Clean a city" 
For example, in english we would say. 
"Once a month everyone in Rwanda leaves their house to clean the city"

Could I say 
"打扫城市“ ”把城市弄干净”？ Or is there  a better way of doing this?
You could use 清洁城市 or 清潔城市.  打扫 also means clean but it is usually used when cleaning (actually sweeping) happens in a smaller area (i.e. cleaning your place / your room etc)