If your 6-week old puppy is dirty or stinky after living six weeks with his litter mates, it might be time to give him a bath. At six weeks old, he is regulating his body temperature quite well and can handle being submerged in a warm bath. If your puppy only needs some spot cleaning, consider just wiping him down with a warm washcloth or dog wipes. But if he needs a full bath, it is safe at this point to give him a warm bath using oatmeal shampoo or tear-free puppy shampoo. If the weather is cool and your home's heat is on, be sure you are drying him well before you set him free to run around or to be with his litter mates again.
If your 6-week old puppy is taking his first bath, he might be nervous. You can warm up the bathroom by running hot water and keeping the door closed before bringing him in. Be sure to fill up the tub or the sink with warm water before introducing your puppy to the bath--the sound of running water may scare your little guy. So, be prepared with your bath before you bring the puppy into the bathroom. Keep the door closed and wrap him up tight while you dry him once he's nice and clean. At six weeks old, you can also give him a treat to reward him for good behavior.