Take the skimmer basket out use a rubber plug for the line. Cut a 8 inch piece off the end of a noodle. Place it in skimmer. Done! Or use a gizmo and call it a day.
I bring my FC to shock level the day before closing. I do not use polyquat 60. People use it for extra insurance against algae. If you close the pool with water temperatures below 60 consistently you should not need this algaecide.
I seal mine off just because I don't want water in my skimmer. It's still plugged with a gizmo though.
Its not necessary to seal it off.. it's just how I like to do things.