An alternative to your toilet bowl approach is to have the mold inverted and fastened on top of the crucible. When everything is molten the only thing you have to do is turn it over.
This technique is used for casting metals in a controlled atmosphere. The crucible and mold assembly is purged with a gas during the melting and tipping operation.
I have visions of the trap in your toilet bowl getting plugged with solidified metal and I don't think the standard rubber toilet bowl plunger will clear it.
