If you decide to use a trash bag, choose thick trash bags. Cat claws can nick thin trash bags so you need heavy duty trash bags. The bag won't fit as comfortably as a liner, which means cutting it into a smaller size. Without a way to secure the bag, like a drawstring you might find yourself dealing with the bag falling back into the litter. Trash bags labelled as compostable will be too thin to work properly as a cat litter liner. Kitty litter is too heavy.