Fortunately, gerbils are not very smelly and their poop is small. But their cages should be cleaned at least every 2 weeks or more often if necessary. Use plain water to wipe down the cage. Throw out old litter and bedding and add new. You can wash food and water bowls with a little dish soap, but rinse and dry very well. While you're cleaning the cage, you can place the gerbil in a smaller cage, a tall bucket that s/he can't escape from or a rolling ball. Make sure the area is safe and secure.