Nappi Nippas are such an amazing invention and fiendishly simple: just a plastic T shape with little claws at each of the three ends.
- Simply hook one claw into the fabric roughly over one thigh (while holding the nappy together with the other hand),
- Stretch the nippa over to the other thigh and catch the claw into the loops of the fabric there,
- Pull the centre claw down to catch at the fabric between the legs.
The resulting grip should be Y shaped if it has enough tension.