I haven't had any luck with the cowboy magic stuff. It just seems to spread stains on my birds. Maybe I just have unusually funky birds. I use tide with bleach alternative to wash them. I wet the bird, then use a very soft toothbrush to gently work the Tide into the feathers, going with the direction of the feather (& using the brush to gently work out any set-in funk in individual feathers). I let it sit on them for a few minutes, then rinse & repeat, if necessary. Works better than anything else I've tried. I've not tried bluing, however, but I have heard that that works really well, too. You just have to be careful not to use to much, or else you end up with a blue bird!
To wash crests on my Polish, I wrap the body of the bird in a towel so I can then use one hand to hold the bird's body, freeing up my other hand to do the washing (usually over a bucket in my kitchen sink so that I have running water to rinse with. shhhh, don't tell my husband!). I then hold the bird on its back, so its head is upside down, to wet & rinse. This way I don't get soap and/or water in the bird's eyes or nostrils.