#1. Seek medical attention. The barb from the sting ray often breaks off in the victim and this needs to be removed. In Puerto Penasco, the red cross will treat your sting ray wound with an anesthetic injection, this will relieve the pain. If you can't get to treatment soon, soak the extremity in fresh water as HOT as you can stand. Heat denatures the poison. This will relieve the pain.
#2. Meat Tenderizer, urinating, tooth paste, rubbing sand into the wound are all anecdotal and may even serve more harm than good. Heat breaks down the poison, ultimately relieving the pain. I know this works from personal experience. Soak the wound in as hot of water you can stand and change the water often to keep the water hot. This will relieve the pain.
#3. Sting Ray wounds are known to produce cardiac dysrhythmias, convulsions, dyspnea, nausea, vomiting, muscle cramps etc. If you are prone to anaphylaxis due to bee stings or other allergic reactions, seek medical attention immediately. Heat breaks down the poison, ultimately relieving the pain. I know this works from personal experience. Soak the wound in as hot of water you can stand and change the water often to keep the water hot. This will relieve the pain. Better yet, don't run the gauntlet.