He's biting because he is frightened.
Very few cavies enjoy getting a bath.
Other people may have their methods, but I'll just relate what works for us. We put a dishpan in the kitchen sink. The only caveat with this is that if your piggy is a jumper, you have to prevent him from jumping out of the pan all the way to the floor. If you are afraid of this, get into the bathtub with the piggy and the dishpan which works well if you have a handheld shower head. But, I digress.
We're back at my kitchen sink which also has a spray attachment. One of my boys is terribly afraid of it so I don't spray him with it. Run enough water in the pan to cover his belly, bum and legs. Gently scoop up water and get him wet. Soap him well, take him out, and put him into a towel. Be sure to cover him with the towel because he will shake like a dog and fling water everywhere. Dump the water, run some clean water, and rinse him thoroughly. Towel dry him to the best of your ability and then use a hairdryer on LOW to dry him. Keep a hand between the dryer and the piggy to monitor the heat. Get him as dry as you possibly can because it takes a while for them to dry down to the skin, especially if they are not short-haired.
Cavies sometimes tremble after the bath.......whether from fright or cold I don't know. If I have one like that, I take the time to cuddle the piggy bundled in a small towel on my chest until the trembling stops. I then put them back in their cage. I try to bathe them early in the day so that they are thoroughly dry by bedtime.
Be sure to use a shampoo made for small animals like
Squeaky Clean. A shampoo made for humans will suds too much and you will have to repetitively rinse them........which you want to avoid. Insofar as the biting goes, I have one who is a biter when he's frightened and I simply wear latex/nitrile gloves.
