Litter boxes - train your human in proper hygeine

Dear George,
I need your advice as soon as possible….before I go completely nuts!
Lately I’m having quite strong arguments with my human over the necessity of a litter box in our house! You see, I’m using the back garden as my litter box but lately my mummy start talking about “potty training” me ….just in case! Mind you….what does she mean by “just in case”?  Could she be up to something? Like leaving and locking me indoor for days? Just the thought of it gives me “goose bumps”! Anyway, when I asked her why do I need to be potty trained she said “what if we need to move from a house to an apartment, a flat”? I don’t get it! Why would we move? But, that’s not the end to our problem. We are dealing with a big dilemma in regards to the litter itself. Neither one of us is knowledgeable enough to make an informed decision. 

 She’s looking for something “natural” and I’m freaking out, twisting myself and turning from side to side (as you can see in the photo attached) to understand what does she mean by “natural”? To me natural is the soil in the back garden. George, seriously what the indoor cats do?
What litter do they use? 
Anxiously yours, 
Lulu 

Dear Lulu,

This tray is far too small

If you are used to using the back garden - soil, leaf litter, or sand - you may just change to ordinary cat litter without trouble, if you become an indoor cat. The most attractive litter to us cats is the small grained clumping kind. Two and a half inches, allowing for a good dig, and an uncovered litter tray as large as your human can buy. It needs to be in a quiet location away from passing humans, dogs, noisy washing machines, outside doors or windows.
If you refuse to change to cat litter, then your human should try putting earth/sand into a tray (with a little bit of poo or pee so it smells correct) and then once the tray is used slowly change that into cat litter. Once you get used to cat litter, rather than earth, you can usually manage to change to litter types - if your human is sensible enough (and they usually are not) to make the change slowly, adding a handful of the new type daily to the old familiar litter. Most of us cats dislike a tray liner: it gets caught in our paws.
My human fosters kittens who come to her using the wooden type

This filthy tray has a horrid lining

cat litter. She changes them slowly to clumping litter (which she prefers) but keeps a second tray with the old wooden litter as well. That means they will be flexible about what they use in their new home. The rule of thumb is one tray per cat and one over. She also sends the kittens to their new home with some soiled litter to be put in the new tray so it smells like a latrine.
Here are some photos of bad litter arrangements. Show them to her.
Yours
George. 
PS. A good human servant cleans out deposits from the tray twice a day.