Master Cylinder
WARNING: This page is about a different car, the 2003 Toyota Prius, 2002 Toyota Prius, and 2001 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
Ensure brake fluid reservoir is full. Disconnect brakelines from master cylinder. Have an assistant slowly depress brake pedal and hold. Block off outlet ports on master cylinder with finger, then have assistant release brake pedal. Repeat 3 or 4 times or until master cylinder is bled.