To sanitize something is to make it extremely clean. After watching you play with your slobbery dog, your fastidious friend might insist that you sanitize your hands before sitting down to dinner.
When you clean or sterilize something, particularly for reasons of good health (like not spreading germs), you can say that you sanitize it. You can also use this verb in a figurative way, whenever you "clean" something: "She doesn't want to risk alienating her audience, so she sanitizes her speech to remove anything that might offend them." The Latin root is sanitas, "health."