I have two litter trays and Lucy has access to outside. In this weather she prefers not to go outside though.

I have read somewhere that it is not advisable to use bleach around cats, particularly in case they walk on it and then clean their paws. (I shall see if I can dig out the paperwork where I read that). I usually use "green" washing up liquid and a bit of elbow grease! Seems to do the trick.