I was having a debate last night with my buddy about why we had enough sap to make 25 gallons of syrup and we only drew off 18. I told him that it takes a bunch of gallons to fill the machine and then a bunch more to evaporate until the first draw and that is our differance. I could find this out a couple of ways. 1 Actually measure how many gallons I used from fill to draw. 2 Pull all the sap from the evaporator measure the volume and sugar content and calculate how many gallons it took to get there. Does anyone have a calculation based on size of the evaporator for this number?