A flatworm has one large single tube as the digestive system. Food is taken in from one end, is digested and nutrients are absorbed inside and the waste is excreted from the other end of the system. Mechanical digestion occurs in the gizzard.
In humans, however, after ingestion food travels much more through the convoluted tubules and food remains in the stomach for a longer time. Mechanical digestion of food occurs in the mouth, passed to the esophagus, then to stomach, small intestine, large intestine and then waste exits through the anus.
