3reds this is what i do for my feeder pails:
i start by bringing a stock pot full of water almost to a boil.
i line my pails up, i put HALF of the sugar required in them. i get my tap water real hot. when the tap water is hot, i stir some very hot top water into the pails with about half the sugar, and then add the near boiling water and the rest of the sugar, and stir. give yourself some room when adding the tap water to add the boiling water to dissolve the crystals and add the rest of the sugar, gradually, and add additional near boiling water from the stove top to top off your pail. i do this one at a time. it is tedious, but it works.
don't put the sugar in last, start with a little sugar then add gradually, and add the hot water from the stove. let it sit after all is stirred up, the crystals will dissolve. don't get the water from the stove too hot, ya don't want to blow out your plastic pail........
hope this helps?!