Why has my cat suddenly taken to shitting in the utility room sink?!

[Gose]

It's weird. He seems perfectly healthy. We have a cat flap, plus doors and windows are permanently open in this weather and with one of us always here.

No change in diet or circumstances. He's getting on a bit but surely it would be easier for him to amble out of the door than to spring up onto the draining board and crouch over the sink?

Is he going outside as normal? If not then I'd assume it's avoiding the outdoors that's the cause.
One of mine refuses to use anything but soil, hence an unusual litter tray for overnight/ bad weather. When dp started working from home pre lockdown, the desk chair became the toilet of choice. It only really ended because the cat realised there were other ways to defend his territory from dp's invasion.

@DanceWithYourBalloon We had a cat that used to wee directly down the drainhole too! His aim was amazing. He also used the loo fortunately so I trained him not to use the plughole because, however good his aim, he started to hop in any sink, not just the shower... He also opened doors, windows (in a tag team with his siblings), knocked on the door to be let in, patted your arm if he wanted attention (or to when he'd had enough), liked riding in the DC's electric car, on the robot hoover, and enjoyed being pushed around in a doll's pram. He was always waiting on the street corner after school for the DC and at the back door at 6pm on the dot everyday when I started cooking dinner. He also knew how to turn taps on for fresh water but never got the hang of turning them off

Have you ever smelled a bathroom that hasn't been used for a long time and the water has evaporated from the U-bend so the pipe links directly to the drains without a waterlock, @Gose? Cats' sensitive noses can smell the drains so the sink smells like a toilet to them. Your cat is probably wondering why you wash up and drink from a loo

That explains why your cat has chosen the sink but not why he has changed habits. It could be ill health or stress or it could be he thinks your litter tray cleaning isn't up to scratch. Or he could just be being a fickle feline.

My cat would piss on the bath mat when she was a kitten.

I think she saw us on the toilet and thought that was the wee room, because she'd sometimes come in and do it when we were on the toilet!

Got rid of the bath mat in the end and there were no more issues.

Can you keep the utility door shut?

Sorry, a bit late to the conversation, but I had a cat who was perfectly house trained. One day started going in the bath, and after a while I realised he was scared of a fox that had taken up in the area so wouldn’t go out at night. Fox soon moved on and he went out again.

My little rag doll cat always poo in the bath or even poo on the bathroom floor, whatever takes her fancy really 🙄
She even uses her litter tray sometimes