i have the same mason finisher/canner, i have not had a problem with niter. i filter at draw-off and again before i start finishing when it is hot. i think this takes care of most of the niter and suspended solids. if i do not start finishing right away i will let the partially finished syrup settle in a draw-off pail, then when finish i am very care to not pour the settled portion of the syrup through my filter into my finisher. you may have more niter in sap than i have but if you filter more i think it will help, and if you clean your finisher after every batch will it is still warm the build up will come off easier. i use warm water, vinegar and a "magic" eraser. this only takes a few minutes and you can start your next batch.
2008 700 ranger xp sap hauler/45 hp 4x4 tractor/028 super stihl
2x4 mason hobby/blower/new for 2014 smoky lake hybrid pan
2014 300ish buckets and still need bigger evaporator/14 x 20 square log shack
2015 2x6 drop flue phaneuf approx. 325 buckets, 1 year older, not sure about the smarter part ?
gets expensive in a hurry!!