Cut the watermelon flesh from the rind, leaving only a 1/4-inch layer of pink flesh on the rind. (Reserve the flesh for another purpose.) Cut the green outer skin from the rind and discard; cut the rind into 1-by-2-inch pieces. Combine the vinegar, sugar, allspice, salt, black and Sichuan peppercorns, cinnamon, ginger and 1/2 cup water in a medium saucepan. Bring to a boil and cook, stirring regularly, until the sugar and salt dissolve, about 5 minutes. Add the watermelon rinds and bring the mixture back to a boil, placing a heavy object such as a heat-proof plate on top to keep the rinds submerged. Reduce the heat and simmer until the rinds are tender when pierced with a fork, about 8 minutes. Remove from the heat and cool completely.
Transfer to airtight containers and cover. Refrigerate at least overnight before serving. The pickled watermelon rinds can be kept in the refrigerator for up to 2 weeks.