I regularly worm all my cats ,4 out of the 5 of them go outside
I have 2 litter trays one beside the outside door in a small porch room and the other up the stairs out of the way along a small landing bit for some cupboards ,they are cleaned regularly but with 5 cats I cant be hanging about keeping an eye on them all the time

even when the trays are empty Kira somtimes has a little dig in them just in case !

She did like the litter trays when we first got her but stoped after I told her off for it ,but lately she has started again ,I just hope she will stop it again