Clean the chitlins thoroughly under cold running water
Soak them in cold water with vinegar or lemon juice for several hours
Rinse and scrub them again, removing any debris or fat
Place them in a large pot and cover with fresh water
Add onion, garlic, salt, and pepper if desired
Bring to a boil, then reduce to a simmer
Cook until tender, usually 3 to 4 hours
Skim off any foam or impurities during cooking
Add more water if needed to keep them covered
Drain well before serving or seasoning further