Anastomosis leak testers for testing for leaks in gastrointestinal anastomoses in patients include an inflation pump and a conduit part. The inflation pump has a compressible portion and a mechanism for providing a uni-directional flow of air through the inflation pump upon intermittent compressing thereof. Conduit parts have an interior space, a portion to be inserted into an anus of a patient or arm to be mated to a gastric tube, rectal tube or endoscope, a pressure relief valve and an indicator pin, and a rearward arm connected to the inflation pump. Upon actuation of the inflation pump, air flows through the inflation pump and through the conduit part into the patient's bowel. When the air pressure in the bowel exceeds a specified pressure, air is released through the pressure relief valve and ejects the indicator pin, which alerts the surgeon that the desired rectal pressure has been reached.