I jut pick them up, like you would a ferret. One hand for little rats, two hands for big fat rats. If they bite, try using gloves, they give up biting once they find out you're not going to squeal and put them back. Are these breeders? Because female rats with babies do get very bitey, and there's no socialization that can help that. Some rat moms are just that way. If the rats are very big (I've had some HUGE male rats in the past) I'd be afraid to pick them up even by the base of the tail. Small rats it's fine. But after they get to a certain weight, I'm sure it hurts them to be handled that way.