Why does he take blood that was thrown on the Mizbe'ach?!
Chizkuni: It was in order to join (Shemen ha'Mishchah) to the Mizbe'ach.
Da'as Zekenim and Hadar Zekenim left this difficult. After Zerikah, its Mitzvah was done, and the Kedushah is gone, e.g. if it spilled on a garment, it need not be washed (Zevachim 93a) (PF).