You get a Schrader style valve that screws into your city water connection. Should be available almost evry where, Walmart, hardware stores,
I apply about 35 pounds of air pressure from compressor. Compressor needs to have sufficient volume. I go through a open each valve one at a time and let blow until water stops coming out.
Dont' forget toilet and outside shower if equipped.
I do drain the water heater first, then blow out hot water lines. I then remove plug from water heater and make sure the all the water is gone from tank.