If they have no taste lingering I just use isoprop.
To get the taste of flavours/liquids out I do a 3-step process:
first soak overnight in Dish soap/hot water, then rinse thoroughly
then soak over night in wate with vinegar, rinse thorougly
then use isoprop, rinse ... ^^
Most stuff can be removed by that
On the other hand I don't bother with sterilizing all too much. VG and PG both are antibacterial. We have a guy in our german vaper forum who conserved his deceased gold fish in PG. I think the fish is in there since 3 years now and shows no sign of degradation ^^. Getting lingering taste out is more important to me, when I reuse bottles....