Stool: Specimen should be collected in sterile bedpan, not contaminated with urine, residual soap, or disinfectants. Those portions of stool that contain pus, blood, or mucus should be transferred to a sterile specimen container.
Rectal swab: Pass swab beyond anal sphincter, carefully rotate, and withdraw. Swabbing of lesions of rectal wall or sigmoid colon during proctoscopy or sigmoidoscopy is preferred.
Duodenal or sigmoid aspirate: Specimen should be collected by a physician trained in this procedure.

https://www.labcorp.com/tests/008144/stool-culture

Note: unpreserved, fresh stool will be rejected.