According to the Torah (see Sefer Vayikra 6:20-21), in the context of discussing a korban hatat – a sin-offering – “Whatsoever shall touch the flesh thereof shall be holy; and when there is sprinkled of the blood upon any garment, thou shalt wash that whereon it was sprinkled in a holy place. But the earthen vessel wherein it is cooked shall be broken; and if it be cooked in a brazen vessel, it shall be scoured, and rinsed in water.”
Thus, if sacrificial blood is absorbed by another object, the laws pertaining to the sacrifice are transferred to the object unless the blood is removed. Specifically, clothing that was stained by blood had to be washed in the Temple courtyard, metal vessels that absorbed blood could be heated until the blood is removed, but earthenware vessels, which retain anything that they absorb, must be destroyed.
Although the pesukim (=verses) that serve as the source for this law deal specifically with a korban hatat, nevertheless the tradition accepted by the Sages is that the rule extends largely to all other sacrifices, as well. The Gemara examines which rules are limited just to the korban hatat and which apply to other situations. The first Mishnah teaches that this law is limited to blood that could be sprinkled on the altar. Thus, if the korban was disqualified for some reason, and the blood could not be sprinkled, or if it had been collected by someone who was unfit to participate in the sacrificial service (see above, daf 15) it also would not need to be cleaned from the priestly clothing. Similarly, if the sprinkling of the blood had already been done by the kohanim, the remnants of the blood would no longer require washing.