Slowly allow it to become a little bit dirtier before you empty it, but
keep an eye out so that your cat doesn't choose to use the little space
between the wardrobe and the dresser. If your weather is clement, put
your cat food dish and tray outside and don't let the cat in for an hour
and a half - two hours after eating. This also solves any smell problem
with allowing the tray to get dirtier.

Once the tray is becoming used infrequently, you can remove it daytime
but if your cat stays in at night, replace it until it is no longer
used.

Most cats are like dogs and will sit and make noises at the door when
they need to. One of my cats uses the letter box and door handle to
attract attention, t'other scratches hell out of the carpet.