Amazon has 2 Pack Straw Cleaner Brush on sale for $2.99.

About this item:

This product includes two reusable metal handled straw cleaners. The brushes are extra long, designed for use with Stanley mugs in 40, 30, and 20 oz sizes. They feature a 10mm wide design suitable for cleaning sippy cups, water bottles, and various tubes. The set comes with clear handles for easy visibility. These brushes are intended for maintaining cleanliness of straws and related drinking accessories.