Thanks for all the recommendations, suggestions and imaginative ideas.
To close out the initial question, my solution was to drain the dehumidifier down the galley sink.
I cleaned out the bilge completely and hooked up the bilge alarm switch to my Victron Cerbo system which I monitor via the internet. I can see the dehumidifier running cycle based on the modulation of the AC supply and I can see when the bilge pump operates. If there is a bilge alarm then an email will be sent to me within minutes.
I would have preferred to dump overboard, but this was extraordinarily awkward to accomplish without making boat modifications that I didn't like. So I am comfortable with this solution.
Thanks again to all.
SV STELLA *****