Everyone's case is different. In my case we camp alot off the power grid back in the woods somewhere and sometimes it gets down below freezing over night.
The BLOW OUT method works best for us as I have a tankless 12VDC compressor and hook up to the city water inlet using a CAMCO Adapter. I can blow out each of my fresh water faucets by opening the faucets until each ones blows air. Then I add a little of PINK ANTIFREEZE to the P-TRAPS...

The beauty of this is the next morning when it gets warm again I can just start using water again from the tanks. Of course if it is going to be a real hard freeze over night I will drain the fresh water tank first then blow out the lines. Then the next day I have to re-fill the fresh water tank.
Never had any problems doing this and have camped out in some pretty cold nights...
When camping off the power grid we dispose of gray and black in totes or dump containers and haul them off to a dump station or bath room somewhere on the sites each day.
I capture all of my gray water using this setup

Our BLACK water is captured in the cassette potty tank which we will carry off to dispose in a dump facility or bath room down their toilet like shown in this google images photo.

Roy Ken