This HummerPlus Brush by Droll Yankees is great for cleaning your hummingbird feeders.  It has soft bristles that won't scratch the inside of your feeders.  The curved 9" brush design cleans interior curves with little effort.  This also effectively cleans the ports on tubular feeders. 

** Clean your hummingbird feeders every 3-5 days to prevent the growth of bacteria.  Wash with hot water and a mild detergent and sanitize with a 50/50 solution of white vinegar and hot water.  Rinse your feeder and brushes well to rid them of any cleaning smell.  Hang the brushes to dry thoroughly before storing away.