Grooming is an activity that is enjoyable for both you and your horse. To untangle a matted tail, wash it with soap and water. Ivory liquid will work well. Rinse and apply a hair conditioner following the instructions on the bottle. Allow the tail to dry and then carefully untangle the mat. A plastic comb with large teeth will work well. You will loose some tail hair as the tangle comes out. For a really bad tangle, repeat the process a couple of times.