Hello Dane,
This engine has basically 6 carburetors (3 carbs with 2 floats each). There are drain plugs for the bowls on each side of the carb which takes a flat head screw driver. Disconnect the battery and remove the plugs, and squirt in mercury's power tune (fill her up) and install the bowl plugs and let it sit 30 min. With plenty of rags, remove the plugs and pump the primer bulb to flush out the carbs. Install the bowl drain plugs on the bottom carbs first after flushing and work your way up flushing each as you go.
Marine Mechanic
30 Year Service Tech Gas/Diesel.