What can i do to get my son to wake up and go to the washroom?

This can be difficult as it is likely your son is a deep sleeper. It may be that his bladder isn't indicating to him to wake up when it's full. What you may want to try to see if it will help to wet less is reduce fluids at least two hours before bed and frequent bathroom breaks before he sleeps. Even with this suggestion, it is a good idea to take him to his pediatrician so that your son can get a physical exam and get a recommendation for treatment.