I have done it with my gf, it's normal than after a certain point the pump starts to pump her inside? I mean, not only her labia, but also her vaginal opening and the first part of her vaginal canal start to swell... it's like her vagina it's been turned inside out, and she become super tight!
We use this >>906442 >>905187 and she fill it
that sound super hot. make you should tkae some pictures. only her snatch.
here's the biggest pumped pussy in video form, the gif i have is too big for 4chan
She can't reach an impressive swell because she can fill the tiny cup in half an hour, but i suppose that the the pumping of her inside prevent to pump well her labia...