If he's only little, the best / safest approach is NOT
bath in a sink or
bath tub , but in a small plastic tub either on the chair or bed next to you (place a towel under it) or on the floor or my fav spot is on the coffee table.
I use a plastic flat bottomed babies
bath for my adult lizards , same deal.
I have empty 2L drink bottles , one full of hot water, the other cold , use these to top up / cool or warm the water in the baby's
bath.
Peppa loves her very rare baths.
Add only enough water premixed hot and cold to get 32-34 degC to come up to his side fringes, if he can stand on the bottom of the tub he'll feel lots more secure.
I'd have some absorbant kitchen paper towel handy , tear off a strip and soak in water , I used this draw water over the back of the dragon or simply have a cup and pour the warm water over the back of the dragon.
The danger in doing this in the sink or
bath is the sound of the taps will freak out a lizard, and a panicked lizard can easily leap out and have a very hard landing on the hard tiled floor and injure itself.