Power steering flush experience

[Roadtreker357]

After reading and YouTube viewing, today I did a good flush on a 2007 Express 3500 (Roadtrek) with hydroboost.

First I just emptied the reservoir, raised the front end, and rotated the steering wheel several times. Looked in the reservoir and it appeared fluid had returned and was going out the outlet. What I expected.

Next I removed the inlet hose and extended it with a clear tube to a jug on the ground. Then plugged the reservoir inlet and filled the reservoir.

With the engine off, rotated the steering wheel several times, but did not see any fluid flow to the jug. Checked the reservoir to find it had over flowed from the top and made a mess. Since the inlet was plugged, the only source of fluid was from backing up the reservoir exit line.

Started the engine, turned the steering wheel, no fluid observed in the clear tube. Slowly pressed the brake pedal to bottom and slowly released to top. Fluid was observed flowing to the jug. Turning the steering wheel lock to lock did not make any fluid flow to the jug. Only pressing and releasing the brake pedal made a flow, and it only flowed on the pedal release, not when applying the brake. After 3.5 qts the fluid looked pretty clear. The end of flushing.

Questions: 1) why did the reservoir overflow with the engine off and after rotating the steering wheel? 2) Why did I only get a flow from operating the brake 3) is there a valid reason for rotating the steering wheel to get a good flush?