Under the head sink.
The pump is located under the sink in the head. It is located on a board mounted on the bulkhead between the head and the hanging locker.There is a strainer connected on the inlet side of the pump that can be accessed easily and needs to be cleaned regularly. It is easier to access this area for servicing through the aft cabin. There is a plastic toggle on the 'drawers' that keeps them from opening fully. Turn it down on the top drawer, let it swing down and you can get at everything without having to stand on your head.If you have a later model 320, there is also a wye valve on the inlet side that will permit you to pump out the reefer. This is a big improvement over the older models that drained into the bilge.The sump doesn't drain fully and some have relocated the drain hole to improve this issue.