i soak my hummingbird feeders in a bucket with a few drops of bleach. But i have extra feeders i got at the local thrift store. So i know they are sanirary to start with.if i bleach.
The wooden ones that are painted or varnished i wipe off with a damp bleach cloth. and if they smell of bleach a hose them off. If they are splattered with droppings i occasionally
soak them in bleach water and hose them off.
I was always told that birds have a very acidic digestive system to help digest seeds and the high acid content kills most germs or virus but i figured just as well be safe.
Here the climate is mostly dry with little humidity but other places i have lived i would get moldy seed if the humidity was high for extended periods. did not want to spread fungus or virus
from the mold so would store excess seed in an old chest freezer.till it was needed.
dklucius