Tell Kate in Vermont that has the frozen windshield washer tank to take a heating pad like the ones you get from any department store or drug store that we use on our sore muscles. Wrap it around the tank on high for a couple hours and it will be thawed.
I usually let it stay frozen until warmer weather comes. If it is half full, I would pour the concentrated stuff in it without mixing it.
Once this is thawed, she should purge all the old mix and replace it with "winter mix’. She has “summer mix” in there apparently.
I’d think a hairdryer or two would be quicker. I’d just take the resivoir outta the car, but then I’m mechanically inclined…