I am having a colonoscopy without sedation tomorrow at 10am and was wondering if it was ok to drink alcohol the following night only 3-4 pints no more?

No: Alcohol is toxic to living tissues (we humans happen to be a complex glob of living tissues), so avoid "moderate drinking." Moderate drinking is too much alcohol. Three or four pints a night is heavy drinking, so nobody should be doing that unless he is weaning down from five pints a night. After coming off alcohol, it really is fine to drink just water, which contains neither calories nor toxins.