Take baths with him. I still take baths with my son almost every day. Helps a lot and makes them feel secure

I have a blow up duck that goes in the bath tub. I think the babies feel more secure other closer boundaries

Yea try getting in with him & putting all his fave toys in there...distract him with things

I dont know what to do either my son three y old n cries murder n the tub 🛀🏻:/

Try singing to him. My son fights me to wash out his hair. So what I do is I sing the ABC song calmly. Being a calm let's them know they're safe and that this change is a good thing. Maybe even reward him afterwards if he goes without the baby bath tub (crying or not.) Just let him know the big bathtub is a good thing.

How about getting in there with him?

You tried bubbles, toys?