Beitzah, Chapter 1, Mishnah 8. This mishnah deals with the laws of sorting on Yom Tov: in what manner a person may separate the waste from the food when preparing his meals on Yom Tov.
"HaBorer kitnis b'Yom Tov":
This refers to a person who separates out the bad pieces mixed into legumes (beans), and does so on Yom Tov. Beis Shammai and Beis Hillel disagree about this law:
"Beis Shammai omrim: borer ochel" - Beis Shammai say that he must select the good food and eat it, and he may not select out the waste. This is the very approach that applies on Shabbos, where one may select the food out of the waste provided that it is done for immediate consumption and by hand.
"U'Beis Hillel omrim: borer k'darko" - Beis Hillel say that he may sort in the usual way. That is, when a few stones or other waste are mixed into the legumes, the natural way is to remove the waste, and so a person may do on Yom Tov.
The utensils with which one may sort:
"B'cheiko" - in his lap.
"B'kanon" - a type of basket.
"U'v'tamchui" - a large bowl.
None of these three are utensils designed for sorting, and so using them involves a measure of deviation from the ordinary way of sorting.
In contrast: "Aval lo b'tavla, v'lo b'nafah, v'lo b'kevarah" - a tavla is a type of table, and a nafah and a kevarah are two kinds of sieves designed from the outset for separating. Using these utensils looks like sorting for future use, and not for the needs of Yom Tov alone, and therefore Beis Hillel forbade them.
The Gemara's precise reading:
The Gemara notes that the permission to select out the waste itself was stated specifically where the food is greater in quantity than the waste. But where the waste is greater than the food, even according to the lenient opinion one must take the small amount of food that is there and leave the waste in its place.
"Af mediach v'sholeh":
Rabban Gamliel adds another method that is permitted on Yom Tov: in certain cases a person pours water over the legumes in the utensil, the waste floats and rises to the top, and he then skims it off and removes it. This too is a manner of sorting and separating that is permitted on Yom Tov.
In summary: In this mishnah we learned the dispute between Beis Shammai and Beis Hillel regarding one who sorts legumes on Yom Tov - whether he may select only the food, as is done on Shabbos, or may sort in the usual way and remove the waste. We saw which utensils are permitted for sorting (one's lap, a kanon and a tamchui) as opposed to those that are forbidden (a tavla, a nafah and a kevarah), which are the classic sorting utensils, the Gemara's precise reading that the permission was stated where the food is greater than the waste, and Rabban Gamliel's words, "af mediach v'sholeh", as an additional manner of sorting permitted on Yom Tov.