Watermelon rind: the disposer is on home ground here, because soft pulp gives way at once. It takes more than one stage: the first breaks, the second reduces, and only then does it flow away. The green rind is hard and thick: cut into strips, it is handled by the two-stage models and up. Whole, it fills the chamber and grinds poorly. Beyond that, it is one of the scraps a disposer deals with every day. If you produce a lot of it, it is worth checking your water utility’s rules.