Is your fitting for your knotmeter?
I did dump a couple of gallons of non-toxic antifreeze into the bilge along with a bottle of citrus cleaner last fall. The sweet smelling pink liquid has remained liquid even with the frigid temperatures we have. I circulated it with my wash down
pump to clean things from the engine mounting to the forward most compartment of the bilge.
I am going to add a true garboard plug, too and remove the "knotmeter"? fitting.
Downeast450