Flux is not so much needed with pure lead. It helps the mixing of alloys. If you put it in lead you will get a nice shiny surface but it will oxidize in a shot time anyway.
On remelting you will get more dross as the surface oxidizes. So when making your ingots theres little point in fluxing. Just remove the worst of the muck and pore it into your ingot mold. I use the hollow of a house brick for this.
As you pore it any impurities will float off and can be shaken off when cool.
“If a cricketer, for instance, suddenly decided to go into a school and batter a lot of people to death with a cricket bat, which he could do very easily, I mean, are you going to ban cricket bats?” :- Prince Philip said after Dunblane