Hummingbirds don’t like dirty feeders, not to mention old hummingbird nectar can make them sick. So cleaning your hummingbird every time you make new hummingbird nectar is important.
First, dump out the old nectar. Then wash with equal parts of hot water and cider vinegar. Allow to soak for a minute if it is very dirty, and use a baby bottle brush to clean inside. Rinse well with hot water and allow to dry upside down on a cloth before refilling.
It is important to not use soap because the leftover soap residue can be harmful for hummingbirds.