I suggest you either fill it to the highest level of the sugar sand build up with sap. Then let it set for 6-8 weeks, dump and rinse. If you can't get that much sap, I'd use white vinegar, even if cut to 50/50 with water. Then mix it to blend. A fire under it to heat it to about 110F then let it set. After 3-4 days check to see if it loosened, if not heat it to about 110-120F again. Let it set 2-3 more days. Repeat as many times as necessary. It will come off. After that rinse well with fresh water, sprinkle in a little baking soda, to neutralize the acid and rinse well with lots of water.
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.