Zevachim 94 - Laundering is a stringency of sin-offering
Even though the Torah talks about blood spattering on a garment, we can generalize it, and include everything that can be laundered like a garment, and everything that can become ritually impure like a garment - since even the smallest piece of a garment is usable and therefore can accept ritual impurity.
If the blood of a sin-offering spattered on a hide, then if the hide was not yet stripped from the animal, it does not require washing (because it cannot be a garment yet), but if it was stripped from the animal, then it does require washing (because the skin can be designated for use as a mat by the owner in his mind) - these are the words of Rabbi Yehudah. However, Rabbi Elazar says that until it becomes a garment, and is not merely designated for use, it cannot accept ritual impurity and thus does not require washing.
Only the place of the blood requires laundering, and it must be done in the Courtyard. So too must the earthenware be shattered in the Courtyard. Thus laundering is a stringency possessed by the sin-offering over other most holy offerings.
Art: Edward Stott - The Washing Day