Brake fluid flush, what do you do?

Gravity bleed will work the same way you you can siphon gas up and out of a tank. If the fluid is flowing, the siphon action will keep it moving. The California Aqueduct is built on this principle to get water over portions of the 4100 foot Tejon Pass. As long as there is fluid in the reservoir and no air bubbles, the fluid will pull itself through the system to a lower level.