What size is the tank? What kind of hides are they? You could try filling the tank with crumpled newspaper or printer paper to give him more cover. Then on monday try and offer him a dead rat. If he doesn't strike, leave it in the tank with him overnight (do this before you go to bed so there isn't a stinky rat sitting in there for more than 10 hours). If it is still there in the morning then toss it. if not, then success!