What is black when clean and white when dirty?

What kind of dog never barks?

I am an odd number. Take away one letter and I become even. What number am I?

Forward I am heavy, but backward I am not. What am I?

I fly at night, I hang upside down, and I am not a bird. What am I?

I'm tall when I'm young and short when I'm old. What am I?

What building has the most stories?