That thing sitting on top of the engine compartment is used to flush the brake fluid.
Changing the brake fluid every brake job is a good idea. Or, every two years or 30,000 miles, especially if you drive down steep inclines on a regular basis. What could happen, if you don’t? A couple of things; Corrosion in the system that can cause expensive anti-lock brake repairs. And in some instances, the brake pedal pressure can drop when the fluid super heats and turns to vapor because of high moisture content.