1) DIFFERENCES FROM KILAYIM (Yerushalmi Halachah 1 Daf 18b)
הכא מקבל עליו ברם תמן ימעט
(a) (The Mishnah taught that if a person sold seeds to his friend, the buyer must accept a quarter of a kav of waste for each se'ah.) Here, the buyer must accept this; there, in Maseches Kilayim (beginning of Chapter 2) the Mishnah rules that if there is 1/4 of a kav of another species of seed mixed into a se'ah of a person's seeds, he must reduce that other species as it is not considered nullified.
הכא ובלבד טנופת ברם תמן מין
(b) Difference #2: Here he must accept only waste but not if other species are mixed in; there, it applies (specifically) to other species.
הכא ובלבד כדרך מגעו ברם תמן ובלבד כדרך משואו.
(c) Difference #3: Here, it only applies to the waste that was present before it was transported (as after it is transported, the waste will collect at the bottom and when a buyer acquires the seeds, it is taken from the top, which he is now expecting to be much clearer of waste.). There (in Kilayim) even after it was transported, the other species (e.g. wheat with barley) will not become naturally separated and he must reduce the other species.
הכא ר"ש מודה ברם תמן ר"ש אומר שני מינין הן ואין מצטרפין.
(d) Difference #4: Here R. Shimon agrees to the law (that he must accept a portion of waste); there, R. Shimon (disagrees and) says that the 1/4 is only prohibited if it is of another species (thereby causing a prohibition of Kilayim- mixed produce).