Cut the fatty tissue in 1/2 inch sized parts
Place half of this in a skillet, with a single layer of fat
Add 1.5 cups water at ambient temperature
Heat the skillet with the fat and water on high, and when boiling, a tat lower
Stir regularly, so that the pieces of fat tissue are exposed to the steam and water throughout
When the water has evaporated (no 'steam vapors can be seen anymore), place the heat on medium and continue to stir the fat pieces now and then
When you see the first fat pieces turning slightly yellow, stop the heating, scoop out the fat tissue with a slotted spoon and reserve
Then pour the fat through a strainer and funnel in a glass jar
Bring the reserved fat pieces back to the skillet and render more fat. Harvest fat maximum twice more. Keep fat separate from the first batch as the quality will be lower, it will be smellier and the color darker.
Store the fat preferably in the refrigerator. It will keep for months