In a large pot, combine 3/4 cup sugar, 10 ounces strawberries, and 6 lemons and 1 lime, both thinly sliced. Mash with a potato masher, 5 minutes. Stir in 6 cups of water and let sit 30 minutes. Pour through a fine-mesh sieve into a large container, pressing on solids to extract as much liquid as possible. Discard solids. Serve over ice. Makes about 6 cups.