My kittens are 5 months old now, fully vaccinated, neutered, chipped etc and have been going outside for about 4 weeks now. They have mastered the art of using the cat flap so can let themselves in and out independently. I have already moved their litter tray to outside the back door about a week or so ago but they are still using it. Anyone know what the next step is? Do I just take it away or should I move it further down the garden.....stop cleaning it out and changing the litter???