Operate a Pumpout
Remove cap from boat's deck waste fitting.
Insert hose nozzle into deck fitting. (You may need an adapter to make it fit. Marinas generally have them available. They are also for sale in boat stores.)
Turn pump on. If there is a hose valve, open it to start suction.
When waste is no longer seen in sightglass, close hose valve, turn off pump and remove nozzle from deck fitting.
Put nozzle (with open valve) in bucket of water for 15 seconds to rinse hose. If desired, rinse boat's tank with water and pump dry.
Close the hose valve. Put away hose. Turn off the pump and replace the deck fitting cap.
For your convenience we have the above How to Operate a Pumpout downloadable in PDF format.