Pour the tonic water into a large jug. Add the caster sugar,
1 tbsp at a time, stirring until it has dissolved before adding
the next spoonful (this should get rid of all the bubbles in
the tonic water too). Stir in the gin.
Cut the grapefruit in half so that you have two quarters.
Squeeze the juice from one quarter into the jug, then
discard the remnants. Using a small serrated knife, cut the
skin from around the remaining quarter and divide the flesh
into two pieces, each with about 3 segments, then cut into
0.3cm-thick slices. These pieces will sit inside your lollies, so
thread them onto the ends of your lolly sticks.
Give the mixture in your jug a final stir then pour into lolly
moulds. Place the sticks in the moulds, then freeze for at
least 6 hours or ideally overnight.
