Leak check with water
It is pretty common for surgeon's to do a leak test during your surgery. My surgeon puts a drain in the stomach and checks labs (amylase) on it the evening of and the next morning to help ensure there isn't a leak. After the morning amylase is back and ok, then oral fluids are started. Since his patients have a drain for a few days post op, the drain also helps to keep an eye on things if there is a leak. If there is a leak, the drainage from the tube will be the color of whatever fluids/shake/milk you have taken in.
honestly, a tube in the nose and a swallow test the next day are pretty old school.
I was reading my post op surgery report and discovered that the Dr. did find a leak when they did the leak test before finishing the surgery. Made me glad that he did it before closing me up. The following morning they had me drink a blue liquid so they could check my drain bag to make sure that there wasn't any more leakage, and two days after I had the Barium Swallow test, so I know I am all buttoned up and ready to go.