Believe it or not, grooming a dog's tail seems to be a controversial subject. Who knew?!
Many dog owners and groomers do very little to a dog's tail in the way of grooming, besides brushing it out, even when the dog is getting a full clip everywhere else! While clipping and trimming the tail as part of a groom seems to be a matter of personal preference for most pet owners, depending on your dog's breed there are strict guidelines for show rings regarding how and whether or not tails should or should not be trimmed.
For most pet owners, however, the main concern is whether or not their dog's tail is clean and mat-free. Tails, like the rest of your dog's body, can form mats, and in fact can be even more prone to collecting debris and sometimes urine and feces, due to their anatomical location. Washing, brushing and trimming your dog's tail may be necessary to keep it clean. Also, most groomers, at the very least, will groom around the base of a dog's tail, to ensure that mats don't for at the tail head and that hair hanging down from the base does not get covered in feces. Depending on your personal preference, your dog's breed, and your overall clipping and grooming strategy, you will need to determine what is the best way to groom your dog's tail so that he looks great from tip to tail.
Your dog’s tail is part of his spine! As such, your dog may be a little reticent about you handling and manipulating his tail, so care should be taken to make this comfortable for your dog. Tails are also prone to injuries; they get stepped on and hit things. When grooming your dog’s tail, be sure to check it for injury before grooming. You don't want to pull hair on a delicate spot and hurt your dog. You may need to get your dog used to having his tail handled if he is not too crazy about this at first, to ease him into the idea of having his tail brushed and trimmed.