Invertagina
1. When a girl pulls her labia outwards to their full extension, and then places them into a penis pump. She will then pump until she can pump no longer, at which point she will double tie(or as many as needed) a rubber band around the lips forming a structure similar in shape to a limp penis.

2.It is the antonym of a mangina
Cindy fucks Steve's mangina with her invertagina thus allowing neither of them to get off.