Cut the green and pink parts from watermelon rind; discard green and pink parts. Cut the white part of the rind into 1-inch pieces; measuring 9 cups. Transfer the rind to a large bowl. Combine the 6 cups water and pickling salt; pour over watermelon rind (add more water, if necessary, to cover rinLet stand at room temperature for 8 hours or overnight. Drain; rinse rind.
In a large Dutch oven, cover watermelon rind with cold water. Bring to a boil. Lower heat and simmer, covered, for 20 to 25 minutes or until tender. Drain.
In a 6-quart to 8-quart kettle or Dutch oven, stir together the sugar, vinegar, the 1-1/2 cups water, and pickling bouquet garni. Bring to a boil. Lower the heat and simmer, uncovered, for 10 minutes.
Add the watermelon rind and lemon juice to the kettle. Bring to a boil. Lower the heat and simmer, covered, for 25 minutes or until rind is clear. Discard bouquet garni.