Tails and manes are tricky, too. Fold the tail in half, approach from the side with a bucket filled with warm soapy water, and dunk the tail in. Shampoo the tail the way you shampoo your hair. Don't scrub too vigorously, or you'll break the hairs. Keep in mind that a wet tail can pack a nasty wallop, so try to hold it still while shampooing and rinsing.
Conditioners are a good idea, especially on the mane and tail.
I have started using a mane and tail conditioner to minimize hair breakage. It's a very good idea if you bathe a horse frequently. Even a good shampoo will strip out some oils, so a conditioner is a good way to replenish those oils and, again, balance the bacteria. Bathing horses will tend to dry out hooves, which can lead to breakage, which might be why dry, brittle hooves are more of a problem in the summer. An easy way to minimize this is to coat the hooves with a petroleum jelly prior to bathing, says The Mane Points publication director Dr. Ken Kopp.