Poopy kitty help!!

[u/Low-Cat-6235]

So I (20,F) own 2 senior cats who I grew up with in a different state. I moved to go to university and when my parents decided to move to a different country, they flew the cats down to me and the share house I live in. I’ve had Pepper (tabby, healthy weight just a big Tom cat, 12) and Coco (small tortie, 12) for 4 months now. I love them very much however I have an issue…
Pepper loves to poop in the bath tub no matter what I do. He has done this all his life and I thought moving would help retrain him but no, he pees in his litter tray (which I keep extremely clean) and poops in the bath. I’ve spotted him pooping in the litter tray a few times mind you but nothing hits like the bath apparently.
Pls send me tips or ways to help him stop. I’ve been cleaning it really thoroughly but it’s still gross lol