I use a scrap piece of wood about 1 inch square and 12 o 16 inches long to flux. I only flux when casting when I fill the pot. Take the stick and put it right in the melt and stir and scrap the sides and bottom. I find it works better than wax, crayons, wood shavings, and Marvelux and I've tried them all.
One word of caution. First time you put the wood in the melt each day, make sure you hold your gloved hand up by the pot in line with your face/body. It will sputter and spit for a few seconds burning the water out, but then it works just fine.