Help with IV Potassium administration

I had a pt who needed yet another Potassium run. She told me that it had burned when a previous nurse had run the potassium. Being a new nurse, I went seeking advise on what rate to run the potassium. I was expecting the nurse I asked to tell me to run it slow but she came into the room with me and set up NS going through a pump and primary line connected to the IV site. She then set up the postassium going throug another pump with its primary line connected to the NS tubing at the port closest to the IV site. I don't remember what rates she set the pumps at but I do know that the patient had no complaints of burning sensation. Can someone help me with what the rates might have been? Would I use the same set-up with a mag run?