It seems like you have a lot of good suggestions, but I just wanted to offer one more. Try filling the tub with balls of newspaper for added security. Keep the balls of paper in the tub for a few days then drop in a rat that is almost ready to be weaned from mom (leave the balled up paper in the tub). I have used this trick for the past two years for a male I have after he has been off feed for approx. 3 months during "breeding season" and it seems to work. Good luck with everything.