The tangy flavor of seasonal rhubarb complements the taste of gin surprisingly well. You can double the quantities for a bigger batch. you can make this beverage without the alcohol, [but why would you?]
4 lb rhubarb stalks, trimmed and cut into 1/2-inch pieces
2 cups sugar
6 cups water
3/4 to 1 cup fresh lime juice
1 (750-ml) bottle good quality gin
1/3 cup Cointreau or other clear orange liqueur (2 1/2 oz; optional)
2 (1-liter) bottles seltzer water, chilled
16 small lime wedges
Bring rhubarb, sugar, and water to a boil in a 5- to 6-quart heavy pot, stirring until sugar is dissolved, then reduce heat and simmer, partially covered, until rhubarb falls apart, about 15 minutes. Remove from heat and cool 15 minutes. Pour mixture into a large fine-mesh sieve set over a large bowl and drain 15 minutes, then press gently on and discard solids. (There will be about 8 cups syrup.) Skim off any foam and cool syrup to room temperature. Pour syrup into 1 or 2 pitchers and chill, uncovered, until cold, about 2 hours. Stir in lime juice (to taste), then gin and Cointreau.
Fill glasses with ice and add rhubarb gin mixture, stopping about 1 inch from rim. Top off with seltzer. Run a wedge of lime around rim of each glass, then squeeze into drink.
Cooks' notes: Rhubarb syrup (without lime juice, gin, or Cointreau) can be made 1 day ahead and chilled, covered, or frozen 1 week. Lime juice, gin, and Cointreau can be stirred into rhubarb syrup 4 hours ahead and chilled, covered.