How to rinse off baby soap during bath time

Hey mummies, hope u all dont find my qns silly. I am a FTM. How do u all rinse off your baby soap during bath time? I have only been pumping a tiny bit of shampoo into the bath tub (taught by confinement nanny). Have been doing this when he was a newborn even to now when he is already 4 months old. Want to put shampoo on his body but I'm struggling to figure out how to keep him soap-free when the soap just wash down his body into the bath tub, which he's sitting in. Also, pls let me know when did u start to put shampoo on ur baby's body? Worry that am i doing this too late? Bc his body has been covered in germs for so long? 🤨