Lead fluxing is a continuous process. I melt all my lead in a 3 quart cast iron Dutch oven and toss a small pea sized lump of wax (crayon piece, paraffin cube, or lump of beeswax) on top of the molten metal. It usually melts and starts to burn so using a long slotted spoon, I stir it till the flames die. The fire is consuming the oxidation so the dirt and contaminates float to the top and I skim them off. I do this 4 or5 times and sometimes more if I'm melting firing range lead. You'll know if it's contaminates, it's not heavy like the metal. I try to limit each pot to approx. 20 pounds because the larger batches are hard to keep stirring without getting my hand too hot in the glove. once I get a liquid mirror appearance on the metal after fluxing, I add the sawdust, borax, or powdered charcoal to prevent oxidation. the liquid metal is poured into ingot molds and cooled for placing on my stack. When it goes into my casting pots, one is a Lyman and the other is RCBS, I flux again , usually twice and add borax or powdered charcoal to prevent oxidation. Every time metal is added to the pot, the fluxing and adding of antioxidants is repeated. I also have shot makers with orifice holes that are super small. They'll clog up a lot faster than the nozzle of a lead pot. With that covered....problems with the lead not coming out of your bottom pour pot can pretty much be narrowed down to contaminants being stuck in the outlet orifice or temperature too low. To clean the contaminates, you have to melt the lead if the pot isn't empty and remove the needle and clean it with steel wool. the seat needs a good cleaning also. Get a good thermometer, either analog or digital that you can measure up to around 800 degrees with and check to see if your pot is getting the lead hot enough. I'm not an equipment evaluator, but I have never had a Lee pot that I could use to pour large jigs or large sinkers with. They didn't give a fast enough flow to prevent wrinkles. If you've covered all those bases, then that lead shielding is probably an alloy that's been contaminated with copper, zinc, or some other wicked metal that makes lead turn into a caster's nightmare.