Have to say that if I'm using old lead, I do melt it beforehand and get rid of most of the oxide and rubbish and then pour it into a Lee ingot mould. I will then use the clean(er) lead in the Lee melting pot. Even so, you still end up with residue that has to be cleaned out from time to time.

Personally, I think the Lee pot has a spout with too small a hole in it and I've drilled it out a size which seems to be a fairly common mod.

Steve.