Time is your friend so when your done with the days cooking drain pan in place. If the sand and scale is a all over the bottom use a shop vac to suck it all out. For really heavey burnt niter dump in the full strength Vinegar until the bottom is about a 1/4 full and go to bed. Next day add water above the side scum level and let sit while you collect. Come back drain into buckets to reuse and scrub it down.
On a average we run 4000 gallons of sap and then soak pans for 2 days. I usually have about a 3/4 to 1" layer of loose sand and niter flakes in my finial finish pan that only a shop vac will clean out if time is a factor. This year with a lot of down time I just fill up to the lip of the pan dump in 10 gallons and let it sit and scrape with metal spatula. SORRY I should have said Burnish the bottom of the pan.