Purity: Ruling on Washing the Back Passage with Water
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 63
If the anus is washed with water, no trace of faeces must remain on it. However, there is no problem if the colour and smell remain. If no particle of faeces remains after the first time it is washed, it is not necessary to rewash it.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)