Article: Lubricate the tip with petroleum jelly or water based lubricant such as “KY jelly."  Lubricating the thermometer will make the experience slightly less uncomfortable for your dog.  If you have a digital thermometer, turn it on and make sure that it is in working order before inserting it into the rectum. Most digital thermometers can read in Fahrenheit or Celsius. Check your thermometer’s directions to figure out how to change the type of reading. Mercury thermometers should be shaken down to the end closest to the mercury tip before inserting to ensure the most accurate reading. The mercury thermometer may have both Fahrenheit and Celsius, you will have to check your particular instrument. Have the other person give the dog a “hug” by placing his or her left arm under the neck of the dog and using his or her left hand to hold the side of the dog's face against the shoulder. Your helper will then place his or her right arm under the belly of the dog just in front of the back legs to keep the dog standing.  It is not uncommon for a dog to want to sit down when they feel a rectal thermometer inserted. If your dog is comfortable lying down and stays there for the temperature taking, then you can leave them lying down. Sitting is not the preferred position because the rectum will not be easily accessible. Be careful not to insert the thermometer too deep, or too shallow, as this will affect the readings. Try to gently insert along the side of the rectum, particularly if there is feces present.  The anus is the opening into the rectum, which is a long tube that collects feces. The anus is a muscular sphincter that relaxes and opens to allow feces to leave the rectum. The sphincter can shut very tightly if the dog is painful or afraid. Avoid forcing the thermometer through the anus, but do aim into the middle of the pucker where you will find the least resistance for your well-lubricated thermometer. Remember to keep your hand steady and the thermometer straight. Be deliberate in your approach. This has probably been a very intrusive and stressful experience for your dog, so be sure to use a soft touch. Clean the thermometer off after use - rubbing alcohol works well.Remember, this is the doggy thermometer for rectal use. It should not get mixed up with thermometers you use for humans.

What is a summary?
Prepare the thermometer. Have another individual restrain the dog's body. Insert the thermometer into the dog's rectum about 1 inch (2.54 cm). Remove the thermometer gently.