I wash mine out with hot water and set them upside down on a towel to drain before a DIY session, then I flip them upright to air dry for a while. Most bottle manufacturers disclaimers say that the bottles they sell are washed clean, but not medically sterile when shipped.
I don't worry much about viruses and bacteria in a
juice that's boiled in an atomizer to make steam right before I
vape it. That, and Nicotine in your DIY ingredients is also deadly to whatever's in the bottle. You could always do an alcohol wash and shake, then dump it out and let them dry.