The muscle that doesn't need a "pump." Stomach! Just look at how it contracts☝🏻 It is these peristaltic movements of the muscular lining of the stomach that deliver the food. Thanks to the parallel secretion of gastric juice, food turns into chyme. It is partially digested food of semi-liquid consistency - a food lump, so to speak. And already the liquid content manages to pass through the pyloric sphincter - the muscular "gate" from the stomach to the duodenum.