How about taking basin and have him stand to the side then give him a bath...don't put him in the tub if he doesn't want to be just yet...when he is a bit older you cant explain things better to him...
hope this helps
His parents of course must insist that he bathe - the method can vary. Let him choose how he will be bathed for now, and eventually he'll relax about using the tub.
What about showering? Get one of those hand held showers that attaches to the shower head and the water is diverted to it when you want it to be. My son was not 3 yet when we had to do that because we were remodeling the bathroom with the only tub in our house. It took a few weeks for him to get used to it but he never went back to baths, he loves to shower. It's faster & uses less water anyway.