Christine, It is with the 2–3 fingers in, reaching as far into the vulva as possible, in the come hither position, push with the face of the palm, cupped over the entrance, it is basically pumping in air so that you can feel and hear the swishing, slightly lifting the hand also. I have small hands so it would be to the back of my palm near the wrist, but you can feel as the juice flows, that you can speed up the pressure builds up. The nearest thing I can think of is like one of those air bed pumps. Tell your BF to keep going until you release continuously. His wrist might get tired but he has to keep going. I’ve had GF’s collapse giggling afterwards, or even stop and jump up and place a finger on the clit and shower all over the room, while running on the spot and laughing hysterically. That was a one-off but quite some shower, lol.

Best of luck, hope you enjoy, Love Brian xx