How did they put up clothes line across NY streets?

An easy way would be to drop two lines from each window (one to lift and the other to be used as the line) then tie the lift line half way along the clothes line (this way you have the loop around the pulley) and then pull them both into the air.

Once it is up, secure it to the wall with nails or screws and tie the lines off.

A solo person could use the fire escape by carrying the middle of the line along with the pulley and fasten it to the other side then walk down back to their side and tie it off.

You need the cooperation of the people on the other side of the your street first. You both drop a long cord from the windows you want to use, cord has to be long enough to go all the way to the street. Tie the end together from the street and attach the clothes line to one end. From the opposite window (to the end you tied the clothes line), pull the cord until the clothesline goes window-to-window. Secure the ends around the pulleys.