Wash and clean thoroughly all pig's bones, trotter and the pork loin in running water.
Place pig's bones, trotter, and pork loin in a large cooking pot and add 1 liter of water. Place on a burner over high heat and bring to a boil.
Once the pot has come to a boil, dump water down the drain. Carefully wash all bones, trotter, and loin under cold running water, removing any bits of dark marrow or coagulated blood.
Place the bones, trotters, and loin again on the cooking pot and add 2 liters of water. Add ginger, garlic, scallions, and onion and boil for 16 hours. Bring to a rolling boil over high heat, skimming off any scum that appears. Place a head lid and let it simmer.
NOTE: If you started boiling late in the day. you can continue the next day.
On the first hour check pork loin if tender and cooked through. If not continue cooking for 30 more minutes until cooked. Remove from pot and place in a container and let it cool down. NOTE: Place in the fridge if to be used the next day as toppings.
After 16 hours the broth should be creamy and white. Strain through a fine-mesh strainer into a clean pot. Discard solids. Do this three times to really strain any bone fragment. Set aside