Cat peeing in bathtub

Ladies help! My husband and I adopted a kitten about 4 months ago. He started off using the litter box perfectly. When we finally let him roam around the house we noticed that he started using the bathroom downstairs so we put another litter box down there. For the past week or so I’ve noticed that he has been peeing in the bathtub but pooping in the litter box. I am 4 months pregnant and really don’t want to get rid of him but I am running out of patience and ideas on how to get him to stop peeing in the bathtub!

Any suggestions on what I can do to get him to stop peeing in the bathtub?