Bring this back up with some findings.

Mine always had a cup or so of water in the cabin step each day when new after drying. Having since broken the float switch and never gotten around to replacing it, I just plugged the outlet line. Step has been dry as a bone all summer now. The plugged line is full of water thou.
I'm thinking with the low thru hull discharge fitting, that water does get splashed into it and then runs down into the pump. Not enough to be pumped out. Sounds like a check valve would be the cure here.

Great idea. Ill have to look at my West Marine catalog tonight.

Ron