Not sure what model Beneteau you are but I thought I had a problem with my fridge drain until I discovered a red gate valve under the sink in the head (B331) - it switches from shower drain to the fridge drain. The pump is common to the two drains. Good luck.The pump is running. Haven't checked the outside thruhull yet.
This is our setup too. The bilge pump also drains the refer. The valve is in the compartment with all the water valves.I think there is a valve located where all the water valves are.. if it's turned one way it drains the fridge and if turned the other way it drains something else