We are continuing in siman 12, where the Chayei Adam wrote that if a fly falls into a liquid, one should remove it with some of the liquid. The Chazon Ish explains that the logic behind this halacha is that the entire taroves is removed, so there is no issue of borrer. The Chazon Ish continues, and points out that if there are multiple flies in the liquid, one cannot remove each fly with some liquid, because the entire top of the liquid is considered to be in a state of taroves.
Another way to understand this halacha is that the reason it is muttar is because removing pesoles along with ochel is not borrer, because one has not actually separated the taroves. According to this explanation, even if there are multiple flies in the liquid, it would be muttar to remove each fly along with some liquid. Rabbi Reingold recommends following the Chazon Ish.
Separating pesoles from pesoles is not assur. For example, the strainer in the drain of the sink serves to separate between the water which is meant to go down the sink and larger items which will be thrown out. Although one is separating between two different items, since they are both pesoles, it is not considered an action of chashivus and it is not considered borrer. On the other hand, separating between ochel and pesoles, or separating between two types of ochel, constitutes the melacha of borrer.
Summary
- One can remove pesoles from a liquid by removing some of the liquid along with the pesoles. The Chazon Ish understands that the reason for this halacha is that the person is removing the entire taroves. If so, if there are multiple pieces of pesoles in the liquid, the entire liquid may be considered a taroves and it will be assur to remove each individual pesoles in the above manner.
- Separating pesoles from pesoles is not assur.