Rinse and scrub the pummelos to remove any wax on the skin.
Using a very sharp kitchen knife, peel off the zest of the pummelo, taking care to include only the colored part of the peel and not the bitter pitch.
Cut the zest into thin slices and set aside for now.
Remove the white pith from the pummelo, and discard. Over a bowl, cut into the membrane to release the flesh. Set that aside for now.
Take the strips of zest and add them to a saucepan. Cover with water and bring to a boil for 2 to 3 minutes. Rinse, and repeat once or twice. This removes most of the bitterness.
Add the pummelo flesh to the pot with the zest, breaking up any chunks as best you can at this point.
Add the lemon juice, rock sugar, and honey.
Cover the entire mixture with about 2-inches of water, and bring to a boil, stirring occasionally.
Add water back in if it evaporates too quickly, and continue to cook for about 30 minutes at a simmer.
At this point, the mixture should be golden, and thick and syrupy in texture, and the fruit broken down. Check to see if you need any more sugar or honey to taste.
Continue to simmer at a low setting for about 2 hours, adding more water as needed if it should evaporate.
Allow the concentrate to cool, and store in a clean covered jar.
To make the tea, use 1 tablespoon for a cup of boiling water. You can drink it hot, or allow it to cool for an iced version of the tea.
The concentrate will last in a covered jar in the fridge for 1 to 2 weeks.