Peel the lemons and grapefruit. Remove as much of the white part of the zest and add the zest in a lockable mixing bowl.
Add the sugar to this. With a muddler, crush the sugar in the zest to release the oils. Allow to stand for a whole 24 hours (shake regularly) to obtain a syrup of the oils and the sugar (oleo saccharum).
Juice the lemons and grapefruit and put it in the syrup made to resolve the last remaining sugar.
Strain the whole and put the liquid in a punch bowl, along with the rum and tea.
Take a silicone baking pan, fill with water and put in the freezer to make a big block of ice.
Let the punch rest for a day. Serve in a punch bowl with a large block of ice …
… and garnish with lemon and grapefruit wedges.