Here, the Mishnah is going to talk about how the laundering of the garment has to be done in the chatzer, in the courtyard of the Beit HaMikdash. It shares this halacha (law) with two other laws. The Mishnah says that whether we’re talking about the blood of the chatat (sin offering) splattered onto cloth, onto sackcloth made from goat hair, or onto soft leather, the laundering of those items has to be done in a holy place, which is the courtyard of the Beit HaMikdash. Likewise, the breaking of the earthenware clay vessel in which the meat of the chatat was cooked also has to be done in the courtyard. The purging and rinsing of a copper vessel in which the meat of the chatat was cooked also has to be done in the courtyard of the Beit HaMikdash.
We learn this from the Pesukim (verses), where they command us to do this in a similar way to the laundering of the garment. So we learn from there that it has to be done in the courtyard of the chatzer. The law that the blood has to be washed out of the garment is a stringency of the korban (offering) chatat over other Kodshei Kodashim (most holy offerings), where the blood does not have to be washed out of the garments onto which it splattered.