Over the last week I had to use 55 gal. drums because of a broken valve on our 275 gallon tote tank. I had 2 full drums and 2 1/2 drums frozen solid. I took the chance and put them in my basement to thaw...only took 2 days. I got to thinking that maybe I should have only filled the full ones half full so I could add fresh sap to help thaw what was frozen....maybe you have some containers you could partially fill to use fresh sap to help thaw what froze. Good luck.
Tapping since 1985 (four generations back to early to mid 1900s). 200-250 taps on buckets and then tubing in the mid 90s. 2013- 275 taps w/sap puller 25 gal. 2014-295 taps w/sap puller 55 ga. (re-tapped to vacuum theory) 2015-330 taps full vac. 65 gal, 2016-400 taps 105 gal, 2017-400 taps 95 gal. 2018-additional 800' mainline and maybe 400 new taps for a total near 800 taps. 2x6 Leader WSE (last year on it) supported by a 250 gph RO.