I keep finding my father in law urinating in the trash can late at night could this be alcoholism and what should i do?

Several possibilitie: Well, it's unlikely that he's an alcoholic if he doesn't drink any alcohol. However, he may have difficulty getting to bathroom in time, he may not know what he's doing (like sleep walking), or this may be early dementia. Does he know that he's doing this? If not, that's worrisome. If yes, does he care? It would be a good idea to get him to see his doctor for a thorough evaluation.

Alcoholism: It certainly be a result of alcoholism or some other medical condition, for instance certain neurological conditions may cause this behavior. Have your father consult his doctor and if he allows go with him to make sure the physician knows all the facts, including how much and how often he drinks. My best.