I do not think gravity would move the fluid. I used to fill the MC have helper pump the pedal and open farthest bleeder then go to closer one ,etc. You have to always keep fluid in MC.
Now many use speed bleeders to eliminate the helper.
http://speedbleeder.com/
Now Like Kube, I use one of these pressure tanks. Made my own cap with a fitting. I hook a clear hose onto each bleeder and simply walk around opening each bleeder untill no bubbles.
The nice thing about a pressure bleeder is any leaks become immediately apparent.
https://www.amazon.com/motive-power-...+power+bleeder
John