Might be to put heat tape along the lines and around any filter that may be at the tank outlet.
In construction equipment, a 50-50 mix of #1 and #2 is used to prevent this. #1 is the thinner of the two. The gelling usually happens at the filter, so if you have some way to temporarily
bypass the filter, or even put a pot of hot water around it, it should help get things going again.
Good Luck!
Dodgeman