Complex sentence: The real Number 6 is subjected to aversion therapy to alter his tastes and instincts, along with this he is averted to do everything left handed and then drugged to wipe his memory of the treatment.
Split into simpler sentences: The real Number 6 is subjected to an intensive course of aversion therapy, altering his tastes and instincts, and training him to do everything left-handed. He is drugged to wipe his memory of the treatment.