Once you put the critter in a smaller tub, you may find that your snake needs two more things. A hiding place - the snake may prefer to ambush their [live] prey. And a dark place, so feed at night and cover the enclosure when you see the snake is active.
And BG recommended aspen bedding. That most likely helped, but they also had mites and respiratory infections that needed treating. Not saying yours has either, but it contributed to my animals not eating.