- Infuse the grapefruit gin: Add grapefruit zest and juice to a large glass jar. Add sugar and gin and stir until sugar is dissolved. Let infuse for 48 hours. Strain gin and discard solids before bottling.
- Assemble the drink: To a lowball glass, add grapefruit gin and top with ice. Top with tonic water and garnish with grapefruit wedge.