Should I drain the unheated waterline to our submersible pump in the winter?
The simplest way to prevent damage to your plumbing in winter is to drain the water from everything. No water inside the line means that nothing can freeze, expand, and destroy. So, yes, draining an unheated waterline is a good idea. (The ideal timing for this depends on the type of fall temperatures your part of cottage country is getting.)
You don’t have to remove the pump, however, to drain the line. On many lakes, submersible pumps can stay underwater all winter. But if your lake experiences severe ice conditions—so that the lake freezes all the way down to the bottom, or ice will tug at the intake line and dislodge even an anchored pump—to be safe, you may want to take your pump out. In that case, flush out all the water by running RV antifreeze through the pump for a few minutes.