I LOVE using a paint tray for their first baths. It's low to the ground, not so deep that they can easily drown while we wait on their feathers, and there is a ramp for them to walk up when they don't want to submerge themselves. I was a bit concerned at how slippery it was, though. Even though it isn't deep, it seems to be a natural reaction for Cheyenne to try and paddle. It looked a little rough on her legs when they would slip out from under her.
So, I added Easy Liner non-adhesive grip mat to the bottom. This is the same stuff I use in her cage on top of a towel to prevent splayed legs, get water runoff, and make cleaning much easier. I had to attach it with velcro strips because it floats in the water and I also needed the option to remove it for cleaning.
Like I said in the last post, Easy Liner makes your life easier! Get some :)