A big pot, lukewarm water. Dunk 'em feet first, and keep their head out. Wash that by hand. Gently rub the dirty spots until they're cleaner.
The first result on google (it's the one from demeterdesign.net) looks like a pretty good walkthrough if you're looking to make them sparkle, but I've only ever washed mine out of necessity, not for show.
I just had to bathe four for the state fair yesterday... It was my first time but they seemed indifferent and one of my Barred rocks seemed to like it
I filled the tub in my spare bathroom with about 4 inches of lukewarm water. I washed their bodies with tear-free kids shampoo and scrubbed their feet with this thing I had that looks like a grout brush but softer... Somewhere between the stiffness of a toothbrush and a grout brush. You can use a large cup to rinse them, or if you have a handheld shower head that works great... That's what I used. Just be careful to keep soap out of their eyes and don't let water get in their little beaks. After their bath I towel dried them, then set them up on the counter for some blow drying. That was taking forever though, so I ended up turning a cardboard box on the side and putting it in front of the bathroom heater vent. I turned it on, monitored to make sure it didn't get to hot for them, and let them dry like that. It took about 15 minutes to get them to damp, then I put them in my old brooder box with some clean shavings and let them air dry the rest of the way.
Overall it was super easy, the drying is just time consuming.
we use puppy shampoo,and yes it takes a while to dry them.i just bathed my Silkie Rooster and he looked so handsome.my husband was amazed how calm he was during the whole affairi thing he knew ,he was going to meet his new Hen.
I also only had to bathe one, once, out of necessity and she was pretty relaxed about it. I was wearing full raingear, expecting a flappy struggle, but she just stood there! I did it in the evening, got her from the coop, hoping she'd be a little more out of it, with the added bonus that this is my friendliest of the chickens. I used warm water in the bathtub, and splashed her up as necessary to get the egg off. No soap here, but I've heard others do. Then I blowdried her, which she didn't seem to mind either. I think she liked the warmth. Although she's giving me the evil eye in this pic