I used a spare 10 gallon tank. Put some bedding in there with some lab block and a hamster water bottle. I got tired of trying to predict how many I needed and worrying if one wasnt gonna eat what I was gonna do with the rat. They eat like hogs too lol so make sure you have a supply of food.
I currently have an all gray rat named Stewart who was a feeder and is kind of becoming a little pet LOL