Dice celery, carrots, onion, potatoes and bell pepper into 1/4-inch pieces. Chop tomatoes; reserve all juice.
Place vegetables, tomatoes with their juice, chicken pieces, parsley and garlic in a 10-quart stockpot. Add water. Season with salt and pepper.
Slowly bring soup to a boil over low heat. Skim off foam that rises to the surface; may have to skim 2 or 3 times.
Partially cover pot and simmer 2 hours. When soup is finished, remove chicken pieces with a slotted spoon.
Let cool.Meanwhile, mash vegetables in the bottom of the pot with the back side of a large cooking spoon or a potato masher.
When chicken has cooled enough to handle, remove skin and bones and return meat to soup.
Notes: Soup is best served the day after it is made. Refrigerate and remove fat that solidifies on the surface of the soup.
Serve soup with rice or small, stubby pasta such as pastina, tubetti or small elbow macaroni. For better flavor, cook the rice or pasta in the soup when reheating. Add freshly grated Parmesan or Romano cheese, if desired.