I soak bottles in hot (not boiling) water, with a squirt of anti bacterial fairy. Then I use a mini bottle brush, followed by a rinse thoroughly under a cold tap. I'm still kicking.
99.99999999% bacteria free as I mix using old Domestos bottles
I do get stomach cramps but at least I know there is no bacteria in there
(kidding btw - I use Harpic bottles)
NB: mega kidding, don't do this shit ffs
I use old spare bottles the VG/PG came in etc....
(re-use coz I'm a tree hugger, naaah just a tight git truth be told)