Mickey, I don't think there is any practical way to get the zinc out, or the lead for that matter. Pour what you got mixed and use it for plinking and then just be careful not to get any more in there. There's an awful lot about casting that I don't know. Certainly fluxing and skimming are recommended to a point but you can also skim the tin and antimony out too, and you may not want that.
The way I cast is very unscientific, but I do try not to melt any zinc in the pot. I use my production pot to melt everything down and test all WW with cutters as has been mentioned. I found the bulk melting in an old frying pan to be counterproductive in the amounts I deal with.
Alan
