Using a 5mm hook, in HDC start with a base of 10 sts. Work in continuous rounds increasing 10 sts each round to 100 sts, about 7 inches in diameter. Work in straight continuous rounds for 12 rounds. Decrease 10 sts on next round to 90 sts. Work in straight continuous rounds for 8 rounds. Decrease 10 sts on next round to 80 sts. Work in straight continuous rounds for 4 rounds. Finish top edge with knitted applied i-cord including a 2-inch loop at the end of round.
Litter bag will be about 11 inches tall when finished.
Update: My husband discovered that the plastic tub that our dishwasher pods come in is a perfect fit to be a rigid liner for the hanging litter bag, making it easier to neatly tuck away the top of the plastic litter bag between the crocheted cover and the pods tub. Genius!