Soak the natural dried casings in clean water for about 5 minutes. Slide one end of the casing onto the spout of a cleaned funnel (you can make one from a plastic bottle), ensuring a generous portion is threaded on—it will gradually slide off during filling. Place the seasoned sausage filling into the funnel. The filling can be uncooperative, so proceed slowly and patiently; you can use a spoon or chopsticks to help. Keep the remaining casing in water to prevent it from drying out and cracking.
Gently push the filling from the top of the casing down towards the bottom, aiming for a moderately firm pack. Avoid using excessive force to prevent bursting. Some air will inevitably get trapped inside; use a needle to prick the casing and release the air, preventing rupture. Afterwards, gently squeeze the filling to compact it further.
Use a needle to prick small holes along the entire filled sausage to release any remaining air and moisture. Then, squeeze the meat inside to make it compact. Finally, tie the sausage into sections approximately 15 cm long using clean, thin string. Once finished, hang the completed sausages in a well-ventilated area to air-dry for preservation. Any leftover casing can be drained (avoid sun exposure) and stored at room temperature for future use.
How to eat them? You probably don't need me to tell you, but a suggestion nonetheless: besides boiling or steaming, you can also pan-fry them with a little oil until cooked. I find that this method makes the sausages more aromatic and incredibly delicious.