My husband did not use his feeding tube for several months, but we were told to flush it once a day with water. The hospital that put the feeding tube in gave his family members a "mini-class" on using the feeding tube before he left the hospital and the doctor ordered 2 nurse visits after he got home so that we could practice and she could check on the healing process. We were also sent home from the hospital with a syringe, clamp, wound cleanser, and gauze to go around the site. I am surprised that you were sent home with no supplies or instructions!
I think you would be fine waiting until Monday. Anesthesia can make you very sleepy for a couple of days! If he is on pain medication, that also knocks you out.
I would just like to add that if you use a syringe to put water in the tube, try to get the air bubbles out of the syringe so that you don't cause any unnecessary air in the stomach.
The worst that can happen if you make any mistakes is that you will cause very mild discomfort or make a bit of a mess!