Good morning ROG:

I don't live in an area that gets real cold very often.  Having said that, we commonly, in the colder months, do a 'winterize-lite' after each trip.  I drain the hot water tank, the main water tank, the low point valves.  I then blow pressurized air through all of the water flow points in the ship (the kitchen sink, toilet, shower, etc.) until each is only blowing air.  About 3 or 4 times, after doing it and moving the rig to storage, I find the toilet has filled with water at some point.  Not sure  if it was when I was driving, when it was sitting or what.

Not sure of the cause.  Thoughts?