Purpose: This phase II clinical trial will track, in real time, the process of anastomotic healing and its associated microbiome by performing serial endoscopic surveillance (SES) following rectal cancer resection. By capturing anastomotic images and the associated microbial and inflammatory mediators from anastomotic fluids via SES performed at three time points following rectal cancer resection, we will correlate healing to microbial composition and inflammatory mediator status. Patients will be randomized and, at each time point, will receive lavage of their anastomosis with either saline or a triple antibiotic solution (ciprofloxacin, metronidazole, neomycin). An anastomotic healing score captured during SES will be compared between the two treatment arms and correlated to microbial and inflammatory mediator analyses of fluid samples to determine how intestinal microbes influence the process of anastomotic healing.