Fill Collins glass with ice. Shake sloe gin and lemon juice and pour into glass. Top with soda. Garnish with lemon wedge or other fruit.
Vary to taste by increasing lemon juice or omitting the simple syrup for a tarter cocktail, or by substituting 1 oz of regular gin for 1 oz of the sloe gin. You may also shake an egg white with the other ingredients for a frothier drink.