I also use Borax on occasion and occasionnaly "wash" the tail as mentionned by flytyer. Borax also kills any critters that may hang about and protects form futue problems with bugs. I guess I've got so many tails that I no longer bother washing until I need to use the hair and/or if I'm going to dye it.
Just remember that not all bucktail is the same.... I've noted this before on prior posts dealing with deer hair in general.
My experience over the years is that the sooner you get to work on the tail, the softer the hair will be, the older/mature deer will have more coarse hair but not necessarily more "bushy" tails.
A lot of the tails that shops get come from "commercial deer farms" and I believe the diet & over all climate they live in affects their skins/hide & hair. I use wild deer (male and does) and with a whole bunch of buddies who are fellow hunters, I get to pick & choose, so I'm picky!
I don't believe tanning makes the hair any more soft than any other manner of preparation (based on experience with both manners), degreasing and quick setup/skinning is more important.
So if you are buying from a shop, "test" out several tails and if you don't find the quality that you are looking for, go to another shop/supplier until you find what you are looking for.
There's a good tail waiting for you out there!
Pete AKA Frenchcreek from Calgary