Do your fluxing with something that doesn't smoke and stink .
MARVELUX Non-Smoking , Non-fuming Oderless flux... every one on this site talks bad about it but it's a commercial flux and it will eliminate all your problems ...Glen E. Fryxell recommends it in his article on casting and fluxing ... just try it ... no flames , fumes, smoke or stink...what's not to like !
I use it and I LIKE it .
Gary