This is just a simple guide to washing you guinea pig. But excessive bathing is far more worse then it is good. Try to only bathe them rarely, since they have natural oils in their fur. The cleaner you keep the cage, the less you will have to bathe them.
Step 1: Get Everything Ready
For giving a Guinea a bath, you cannot use human shampoos. Your going to need some Guinea Pig shampoo, which you can ask your exotic veterinarian for recommendations. You will need a large towel and a smaller one. And a small cup for pouring water. Then choose where you will give your piggy a bath, in a sink or bathtub. A bathtub is probably a better choice, so they can't climb out. Fill up the bathtub with one and a half inches of warm water.
Step 2: Introduction
Now, take your Guinea pig to the bathing area. Take it and put the piggy in the water. Give it a minute to adjust to the new, wet environment.
Step 3: Lather and Rinse
Now take your cup and pour over your guinea pig gently and close to the body. Do not go over the neck just yet. Now at this part listen to what the bottle says, probably to just lather into your guinea pig. After your done with that, take the cup and wash all the soap out of the coat. When wash your pig, give treats to calm your piggy's nerves. Make sure to keep shampoo and water away from the pigs face.
Step 4: Dry and Clean
Take your guinea pig and dry it thoroughly. After that take a damp cloth and clean their face. After that comb them and put your piggy back in it's cage. But make sure the cage is clean, because then the bath would be useless.