Lie on your back and bring your knees in toward your chest. Insert one or two fingers deeply into your vagina. As you withdraw your finger, press against the front of your vagina and urethra and curl your finger in a beckoning gesture.
With this motion it’s normal to feel a slight urgency to urinate at first, but with practice and several sessions, you can expect to experience a warm, pleasurable experience.
Try it with only one leg bent to your chest, extending the other, for a variation on the sensation.