Hilchos Maasei Hakarbanos 5:17

Regarding firstborn animals, animal tithes and the korban Pesach, the blood of each of these is given to the altar in one shot by pouring it opposite the foundation, in any direction he chooses, on the three corners of the altar. This excludes the southeastern corner, which didn’t have a foundation, as was discussed in Hilchos Beis Habechirah. We know that it’s all done at once from Numbers 18:17. Regarding firstborn animals, it says, “You shall throw its blood on the altar.” Our oral tradition teaches that the same rule applies to animal tithes and the korban Pesach, whose blood is also given in one shot.

Hilchos Maasei Hakarbanos 5:18

The organs and fats of all offerings are burned on the altar first thing after sprinkling the blood. All sacrifices are skinned, after which the organs and fats are removed; they may not be skinned until the blood has been sprinkled. The exception is sin offerings that are burned, which are not skinned at all, as per Leviticus 16:27: “their hides and their flesh (shall be burned).” We see that the blood is sprinkled first, after which the animal is skinned and opened, and then the organs and fats are removed and burned.