The idea here is that you pivot your pelvis so that it is parallel to the floor rather than sloping back to front. This lets it rotate properly when you run and engages your core muscles. This is where I learned I had been doing it wrong this whole time. I was clenching my stomach muscles to pull my pelvis and my glutes to push it. Both are completely wrong and explains why my butt always hurts after long runs. Your butt should be very loose and you hold your core lightly, as if you were sitting up in the chair and not letting your back touch.
When you are standing properly with your pelvis leveled you should be able to reach behind you and use your knuckles to lightly punch your gluts. They should jiggle like jelly, not be as hard as rocks.
You can read more about Chi posture here, on Danny Dreyer’s site.
My Disclaimer: I am not a Chi Running instructor or an expert runner or a coaching professional of any kind. These represent my notes, primarily for my own edification. If they are helpful to you then that is great and I am glad for that, but I don’t guarantee that everything here is absolutely accurate as they are a reflection of my own experience and memory.