First, turn off power and the water supply to the water heater, and drain it. To do this, attach a hose to the drain valve on the tank, open all of the hot water faucets in the house. Actually, only one has to be opened to drain the tank, but all faucets should be left open. To drain the cold water lines, turn off the main supply line, open all faucets. Since there may be low points in the line that will not drain by gravity, compressed air should be applied to the lines, both hot and cold. Drain the toilet(s) and plunge as much water from the bowl as possible. Pour RV anti freeze in the toilets and all other drains so the traps all are protected. This includes showers, tubs, sinks and basins, and any floor drains. Be sure if you have outside hose bibs that they are open and that no hoses are connected to them. This should take care of the plumbing during the winter.