I used to do this to an old girl, it was her that showed me what to do. She still had a decent amount of labia for her age and when I got the distance just right her labia would rattle so much that her clitoris would move about with the continual tweaking. She enjoyed it very much and always wanted to be entered immediately after she came which was new to me.
When I was like 12 or 13 i walked in to my older sister do this in her bedroom. Was curious why the vacuum was running for so long. Went to investigate and got a view. Seen her out of control bush and her pierced nipples. Then got screamed at by her, then later my mom when she got home.