For my assault on NYC I will bring along several priests to bless the water system, rendering every outlet, faucet, sprinkler system able to pump the Holy Water.
For Street cleansing we would hookup our lines to the hydrants and blast em with a virtually endless supply of water. As we clear around large high rises we will set off the sprinkler system within the buildings, rendering any animated zombie harmless.
The more difficult will be the underground assualts (i.e. subway systems, parking garages etc...) For this we will bring along several of these puppies:
Subway systems will require Shotguns and our water pistols.
Now for aerial assults we will have spray plane pilots stationed on local airstrips outside of town where they will refuel their planes and holy water. A priest will be at each airfield. We will be able to coordinate attacks via radio and will be primarily used as blanket attacks on streets and open fields where large numbers may amass.
Don't be fooled, this is no easy task, NYC is home to millions and in an event like this dissenters and slackers will be left to dry.