I gave up running antifreeze through the freshwater system a couple of years ago. Instead, I drain the tank and all the lines as thoroughly as possible. The quick-connect Whale fittings I replumbed the boat with make this an easy chore. By disconnecting the tubing at the low spots I can get virtually all the water out of the system. I’ll disconnect the diaphragm freshwater pump and run that for a few seconds to clear the water out of its chambers, and then drain the water heater tank.
All this water runs straight into the bilge sump, where I’ll add a healthy shot of biodegradable bilge cleaner and scrub the bilge before pumping it out. I leave the pump disconnected and the faucets open, and that’s that.
I disconnect the heads intake pipe, insert it into a jug of non-toxic antifreeze and pump it through the toilet until there’s a few inches in the bowl.
And that is pretty much that.
I’ve never had a problem with leaving electronics on board over a Northeastern winter, though I’ll unmount the chart plotter and take it and the Tacktick instrument displays home. I always remove both house batteries and the cranking battery and store them in the basement over the winter, trickle charging them once a month and making sure the electrolytes are topped up.
A squirt of Boeshield T-9 or CRC contact cleaner on electrical connections is not a bad idea. In any case, now is a good time to inspect the cables leading to essentials like the bilge pump(s). If there’s any hint of corrosion on the connectors, either cut them off and install new ones, or rub them with a piece of wet & dry until they’re bright and shiny again.
All this is just the tip of the winterizing iceberg. There is much more to do. But if you’ve taken care of these three departments, you’ll sleep soundly even if you’ve been too lazy to do anything else.