For winterizing your fresh water system you will need a few items.
The number one items to have is RV type antifreeze. This year I bough my four gallons at Wal*Mart of all places. You really don't need to pay West Marine prices for -50 rated propylene glycol for use in water systems.
NEVER use ethylene glycol that is designed for use in automotive engines. It is poisonous! Propylene glycol usually comes in windshield washer bottles and ethylene glycol generally comes in Prestone or Peak type bottles.
Using the method outlined below the RV type antifreeze is sucked through the system pipes only, and the tanks are left dry and drained with no antifreeze to purge in the spring.
You will also want a section of hose and the associated fittings to bypass your hot water heater so it too has no antifreeze in it for spring purging.
Some other items to consider would be a five gallon bucket, turkey baster, screw driver and some spare hose of the same diameter as your plumbing system.
Why don't I just blow the lines out with air? While this technique may work on some boats it does not successfully work on all boats. Also most boat owners generally don't have large enough portable compressors to facilitate doing so. The Maine based boat yard we use for storage winterizes over 200 boats and they blow out none of them. Every boat has antifreeze sucked through the pipes because it is far more reliable.