Can you fine him if the sewage is blocked due to the sewage discharge in the restaurant?

No, first of all, you must confirm who you are, fines are the right of the state law enforcement administrative organs, and no other individual or unit has the right to fine. It is normal for restaurants to discharge sewage, and the water bill it pays includes sewage charges, and the sewer blockage is caused by inadequate municipal management, which has nothing to do with the restaurant.

This private person does not have the right to fine, you report it to the environmental protection department, they have the power to enforce the law.