I have never drained my pans after getting them sweet. However I never started without enough to boil at least 3 full hours hard. If you boiled that long, you have enough sweet to protect the pans. They will get some slush on top but will not freeze solid. However, when that happens, I do start a small fire and let it burn out each day. I also don't leave 2" deep in my pans, since I learned how much evaporation occurs after the last fueling. I try to leave it so I am between 1" down to 1/2" in the pans.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.