Regarding water, both hoses off, then pull recoil with ignition off until nothing comes out the high pressure quick connect for the outlet hose. Takes about 3 pulls and works great, zero chemicals. Has never not worked, never any freeze damage.
For the fuel, I'll either run double Stabil in the fuel, then run the engine to get that into the carb, and then drain the tank and the carb fully. That way the fuel in the jets, ports, and orifices is at least treated. Or, I really try to run all of my seasonal engines on 100LL aviation fuel, since it does not go stale. Easy for me to obtain from a local community airport, has a credit card pump which is available 24/7.
Be sure to hold up and drain the wand and hoses as well.