Hang the new bag first while line is clamped, clean the port that is closest to the patient and attach an Empty syringe, pinch the tubing so that nothing goes into the patient while releasing clamp and pulling the air out of the tube via syringe. You may need more than one syringe or simply detach syringe and push the air out of it it before cleaning the port and re-attaching. Once the tube is full of saline, you can release the line. Keep the flush attached in case you will need to push saline to unclog blood clots that may have formed while the bag was dry. You're welcome.