I have been told before that bleach has a similar enzyme in it to cat urine which will make them think another cat is around. This is why it's recommended not to clean up cat wee with bleach as it usually just makes the cat wee more to scent mark. Washing up liquid should be ok for washing their trays out.

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Owned by Ratty girls Hera, Athena, Boomer and Kitty the Cat
RIP Apollo and Starbuck, together again at the Rainbow Bridge. Till we meet again.