^ not easy but most likely kisame his water can blast away the poison and most weapons that come at him and iron sand uses chakra as a magnetic force so he can absorb the chakra. Not that it would be easy because it wouldnt sooo kisame mid-high diff
sasori uses magnet force to make samehada useless and since he has iron sand gaara-style nothing else kisame has suffices to take him out. he cant even drown him since sasoris not alive