I have used a few. I like the feel of the coat after using Carr Day Martin shampoo. But for a clean grey I tend to use a mix of this with Tesco Shampoo (the cheapo stuff!) which is excellent! For a really gross tail I shampoo as above then put on some purple hair shampoo stuff (for old ladies!) and leave for a few minutes.
Quiksilver, and for tails, first dunk the tail in hot water and Napisan, careful of the dock, then rinse, then washing up liquid all over the top and lengths, rinse, then Quiksilver, and then lather in conditioner.