98:7 It is permitted to separate beans that one needs for the same day (even if not for immediate use – Mishnah Brurah 510:7), but one may not use a sieve or a screen, nor may the beans be placed in the water in order to make the undesirable matter or the desired portion float to the top. Rather, one must separate them by hand and pick out that which is easier for him. If it's easier to pick out the undesirable matter, he should do that. If it's easier to pick out the desired portion, he should do that. (If they are equal, he can pick out whichever one he wants – MB 510:8.)
98:8 If one wants to re-sift flour that was already sifted (using a sieve no finer than originally used – MB 506:14), it should be done by a non-Jew or in an unusual manner. For example, one might sift it through the back of the sieve. One should likewise do this with ground matzah. Flour that has not yet been sifted may only be sifted by a non-Jew and in an unusual manner. It is prohibited to separate the undesirable matter from the flour, such as if something fell into the flour. Even to separate the large pieces from broken matzah is not allowed.