Juice the fruit and pour into a 6-8 litre lidded pan with the water.
Chop the inner membranes finely and place them with the pips into a muslin bag.
Shred the peel, add it to the pan, and soak for several hours or overnight.
Simmer the lidded pan gently for two hours until the peel is very tender.
Heat the sugar in a baking dish in the oven at 140°C for a few minutes.
Squeeze the liquid from the muslin bag through a sieve into the pan.
Ensure the mixture weighs no more than 1.4kg, reducing further if necessary.
Dissolve the warm sugar into the pan and bring to a rolling boil until it reaches setting point.
Cool for 10 minutes, remove scum, and stir in the chosen spirit.
Pour the mixture into sterilised jars and seal.