I shock using bleach, 24 hours later, drain below the skimmer/return, leave both open so accumulated rain and snow water just falls out (AG pool), drain and take equipment (not filter) inside. DONE.
I hook up my equipment early in spring, catch all that rain to get the pool filled, turn it on and add bleach and throw in the vac - DONE.
If you open early enough, there's no mess since algae needs relatively warm temps to form.