Not even sure if ablutions is the correct word 
I'm so very sick of emptying the cat tray; my first two cats happily go outside for a poo (in my garden, not other people's).
My latest two, now 10 months old, refuse to understand.
We've taught them the cat flap which they use though they prefer to be in the house mainly. We've moved the litter tray into just in front of the cat flap.
When we're in the house we put the litter tray outside. They complain very loudly and try to shit in the house. After we take them outside about 15 times eventually they go in the litter tray out there.
We thought we were making progress that way over a weekend and so took the tray away (having sprinkled litter around all our borders for encouragement). We came home to shits all round the house 
Please help!
I've had many cats but all my previous ones have been happy to go outside and have never missed their tray....