The simple method is Meths, pure and simple, I put the tail and meths in an old clean coffee jar, FILL with meths, lid on and leave for about 3 weeks...4 max, turn/shake every couple of days.
Extract from meths, ring out tail and retain, and filter, all meths for the next one.
Wash tail thoroughly in MILD shampoo and leave to dry naturally, kneading regularly to stop it going hard and brittle.
Easy!