When we started training ours we removed the litter tray completely - if they have the choice they will go to the tray which is familiar (that is the recommendation on the instructions anyway)

We didn't have any issues with them not knowing where it was or what to do as their tray had always been in the downstairs loo anyway.

I think we are doing great with it, we have 3 cats and one litter kwitter (on the downstairs loo) and *touch wood* we have had no incidents - they have all been great, even Rosie who is only 4 mths old.

Good luck with it