Mimanifshach if you are trying to take only the fly that is psoless meochel and if you want liquid too then that is bkli.
On second thought, if you are taking some of the liquid with it then it is ochel mitoch ochel, soup from soup which isn’t even considered separating and is muttar irregardless of the method performed. But since that liquid itself may now be disgusting and discarded that liquid itself should be considered psoless.