When I do just one bird, I heat water in my tea kettle, and pour it over the bird in the sink. I refill the kettle with hot tap water, put it back on the stove, and by the time I've gotten the first bunch of feathers out, it's hot again. Then I pour it over the spots I missed the first time.
I have a divided sink in my kitchen, last time I butchered, I filled one side about half way with hot tap water, and boiled a good size saucepan of water on the stove, added to to the water in the sink. That brought it up to about 150F, I added another tea-kettle full, that kicked it up to 160F. I swished the birds around in that. I had to let them soak a little while to get the feathers good and loose. The birds themselves lowered the temp a bit when I put them in. I was only doing two. I let one soak while plucking the other, then switched them. Back and forth until both were clean. It didn't take as long as it sounds like.