I guess I would myself an experienced "chicken-bather".
My son started out with 7 chickens about a year and a half ago, and the flock has grown to 15 now. He shows them in the local 4-H, so we've bathed them a few times for various events. For the most part, I think the hardest part is the setup and cleanup. The actual bathing goes fairly smoothly, so long as you prevent the birds from flapping around as they become acclimated.
I use three rubbermaid tubs, each for a different purpose. The trick is getting all the chickens through before the water gets too cold. Obviously, the early bathers get the advantage of most comfortable temperatures and cleanest water conditions. The first tub is the wash station, the second tub is the pre-rinse area, and the third is the final rinse. I looked online to find directions on what to use for each tub, and used a combination of techniques that I think does a good job for blue-ish or light-colored birds. (We have Blue Andalusians and Blue Orpingtons, btw; saving the darkest birds for last.) As long as you hold each chicken securely in your hand, so it feels safe, they seem to enjoy the warm water and tend to relax fairly easily as you wash them. (They do have a tendency to fall asleep so be careful to hold their head out of the water!)
I always wash the lightest colored birds first, as they always look the dirtiest, anyway. Black or dark-colored feathers have the ability to withstand a bath in "dirty" water without showing it a lot better than white or light-colored ones. In the wash tub, I use liquid Ivory soap mixed with a small amount of 20 Mule Team Borax. I usually start out dunking the bird's body and swishing them around in the water, and then I gently rub their feathers clean with my fingers. I even use a nail brush to rub their submerged legs and feet, which they don't mind at all. I sometimes use a washcloth to rub their faces, paying particular attention to their wattles, combs, and earlobes.
Once they seem relatively clean, I rinse them off in the second tub of plain water, but with a capful of Clorox bleach added to the water (to help in the control of mites and lice). The third tub contains some extra ingredients to add some finishing effects and heighten their coloring. The water contains vinegar and a tiny bit of glycerin to give their feathers that "show shine", as well as a dash of "bluing"; which is particularly useful if you have white or light-colored birds. (I figure it may even help bring out the blues of our breeds, as well.)
It's important to towel dry each chicken as much as possible, as you remove them from the bath. They should be placed in a clean, warm (draft-free) area to continue drying. On a warm day, you could put them outside in the sun; but if it's windy they could still become chilled. I usually put them in cages inside the house, near a heat vent, or in a warm bathroom with a small heater blowing on them. I also have a blow-dryer to use on them after I finish bathing everyone. For a group of birds, it's helpful (maybe even necessary) to have a "helper" who can start drying each bird as they come out of the final rinse. Otherwise, the water in the tubs can become too cold before you finish all the birds.
This is what seems to work for us and our birds. If nothing else, it makes for a good story for my husband to tell at work... Evidently, his friends can't believe the crazy stuff his wife does! =P
