Remove rind from watermelon. Peel off outside skin, then cut rind into 3" strips (there should be 12 cups of cut-up rind). Place strips in a large jar. Cover with water to which 1 c. salt has been added. Let stand overnight.
The next morning, drain off all water. Place rind and 2 qts. fresh water in a large saucepan. Boil for 10 minutes. Drain.