A dirty grater can often pull you out of cooking a lot of dishes. The fact that what you eat is in direct contact with the grater makes you want to not eat anything when the grater is all dirty and slimy. Thus, you want to make it look clean. Since the grater has a lot of different hooks and edges coming out of it, you wouldn't want to clean it with your naked hands due to risk of injury.
Thus, the best way to clean a grater is to make raw chunks of potato go through it. Grating raw chunks of potato will clear away all the slime from the grater and will make it look interesting and cleaner. Your grater deserves better care than this and you should be giving that to it. Clean your grater through this method regularly.