That's what I usually do but I have let them build up and it would be a pain washing by hand. I was also thinking of spraying them out and boiling them for a little.
I just spray them with the sink sprayer using full hot water. Shake them out and let them dry for a day on paper towels.
If trying to get rid of a strong flavor I will rinse with isopropyl alc after rinsing with water. And let dry for at least a day to be sure that all the iso alc is evaporated.
that is when I do wash them. If not changing flavors I very seldom wash them. the 6 120 ml bottles I use for my Cromwell's Custard have not actually been washed in over a year for sure. I wipe the outsides down with alc on a paper towel if they get gunky from drippings or something.
I only use plastic juice bottles for my out and about bag supplies.
Pretty much clean them the same way though. But a bit more often.