I used to use corn strarch on my horses white socks and it worked great! I've never had a horse with a white tail, but I assume it would work on a tail as well. How you use it on the socks is you wash the sock, then mix the corn strarch w/ water to form a paste. You pack the paste on the wet leg and let the corn strarch dry. Then when it's dry, you brush it off and you have a nice white sock!