Grady Head discharge

it depends on the model and year. My 272 discharges to a deck pump out fitting on the starboard walk around deck between the cabin wall and the outer hand rail . I do not have a "Y" valve to dump my holding tank overboard.
 
The waste cap is usually topside toward front on either side depending upon model. The thru hole is usually just to the side of the centerline about mid section of the boat.
 
no it pumps out the bottom,the sea cock on my boat is about center , 3 feet fowrard of the head.