Rinse the rice in several changes of cold water. Drain completely in a mesh strainer and place into a large pot. Stir the vegetable oil into the rice and set aside for 10 minutes.
Stir 6 cups of water, the bouillon cube, char siu, and green onion into the rice. Bring to a boil over high heat; reduce heat to medium-low, cover, and simmer 1 1/2 hours. Stir frequently as the rice cooks to help break the rice grains apart and keep it from burning on the bottom.
Stir in the remaining 2 cups of water and the century egg. Continue cooking another 1 1/2 hours, stirring frequently until the congee reaches your desired consistency. The congee is ready when the individual grains of rice are no longer discernable and have thickened the soup.
