I didn't actually post the photos because by the end of yesterday I was so grossed out that I couldn't look at them and I didn't think anyone else would want to either.
So please stop reading now if you don't want to look at photos.
I should tell you that there were some tails that the abattoir blokes had cleaned up for me (which is lovely of them to have done when I wasn't being charged for them), but the truck driver didn't know that he was supposed to pick up tails and they went feral (or should that be more feral?). So I got these 'fresh' ones.
I meant it - I'm going to post the photos.
I didn't take many because once my hands were dirty there was no way I was going to touch my camera, but these are what I have.
After the first rinse and swish. I'm sort of sorry I can't embed the overpowering smell to go with these. Believe me the experience is missing something (thankfully).

A close up, trying to show the cloddy matter I was dealing with:-

My very brave mother helped with the first rinse:-

I still need to wash them again. Probably will put lots of conditioner in and comb them through to get the last bits of chaff out. Then I'm going to get some hair dye (one that covers grey) and try to make them all black. Then I have to attach them to the tape. This should be interesting.
So when you discover that it costs one hundred dollars to get real horse hair it is worth it. There is a reason that it is expensive. Either pay up the bucks or go with the knitting cotton option.
The chance that anything in life is free?
... Approximately None. This mane and tail were very dearly bought.
And on a related matter it seems tentatively possible that the scent of soap and hand cream has masked the smell of manure.