In southern California there’s a good chance of getting our first rain this weekend! (Very needed in our drought-ravaged region.)
I learned from Mike at Pacific Plumeria to let your container plants stay out in a rain or two before storing them (if you do), as the pure rain water will help to wash out all the collected salts in the pots from tap water use throughout the year. Of course, too much of a good thing is not good, since plumerias don’t need water while they’re dormant.
If you live in a mild winter zone (like the coast of California) and leave your pots out over winter, then you can fill them with mulch/soil so that when it does rain, too much water won’t collect in there.