Then buy Napisan, as hot water as you can stand with Napisan in it, dunk the ends of the tail for as long as you can hold the bucket up. Repeat if the water is really yucky.
Wash with QuikSilver, leave for a couple of minutes. Wash that out then slap LOADS of conditioner on it, any one will do.
Pop it in a loose plait and into the tail bag, and repeat the process weekly/fortnightly, then eventually the lovely white hair that has never got dirty will grow down, and the yellow will grow out.
Another vote for tailbags. Chancer has his bagged in his tailgator one all the time but in the summer I leave out the top third as a swisher. He had a black tail
but it is very long and thick and he stands on it.
I can also recommend very hot water and equine blue - soak tail to below a few inches below the dock for 10 minutes. Also put equine blue in the shampoo and conditioner - get it from equineblue.com - old dolly bag stuff.
Another great whitener is persil washing liquid mixed with a little shampoo and equine blue - you can also add a little vanish - but never use on the dock.
Sorry to hijack post but we also have the problem of a very thick and very yellow-ish tail..where can I get one of the tail bags you're talking about from??
These are the tailgator ones - I also helped them develop the mane bags if you have a horse with a long mane. Chancer's has never rubbed his tail and I have the folded version which I personally prefer as his tail is very long.
If you also buy the survivor detangler - this keeps the tail in great conditon and those with white tails have said helps with the yellow pee at the top of the tail mares have.
Another vote for tailbags and mane bags, my grey shetlands mane and tail stays white and they stop her mane getting hitched up in harness and reins. You can leave them in for two weeks they are a real time saver wouldnt be without mine.