Head hoses/valves
On my 281 there are two throughhulls with valves to the left of the head. The forwardmost is the raw water intake for the head. It brings in saltwater when you pump/flush the head. The rearmost hose/valve is the head discharge leading to sea. It is not legal to use that and dump sewage within the three mile coastal limits of the US. There is a third hose which goes through the aft bulkhead and leads into the cockpit sail locker. There it goes into a Y valve. This hose takes the sewage from the head when it is flushed to the Y-valve. When the valve is in the forward position (there is a silver metal piece which can be switched) the head dumps overboard through the through hull in the head. When the Y-valve is switched to the aft position, the head dumps into the holding tank in the back of the sail locker. The tank is then pumped out via the black screw cap on the stern deck.