I was ezAll Total Body wash on my palomino gelding. I pour a little of the concentrate directly on the mane/tail and work it in. Let it set for about 5 minutes and rinse thoroughly. For me,this stuff is amazing how well it removes dirt & grime. Then if needed, I use a whitening shampoo, let it set for a few minutes also and rinse. Last, I use a good conditioner. His mane and tail come out sparkling white. In the springtime, it may take 2 washes to get the winter gunk out of his tail.
I've never used a tail bag, so I'm no help there.
"SUCCESS is not what horse you have . . . but what you do with that horse."