SHAFAQNA – The Grand Ayatollah Makarem Shirazi answered a question about the duty of a person when he/she finds out that the Torbah (Torbat) of Imam Hussain (AS) has become unclean.
Question: What is our duty if the Torbah of Imam Hussain (AS) becomes unclean (Najis)?
The Grand Ayatollah Makarem: To make the Torbah of Imam Hussain (AS) unclean (Najis) is Haram, and making it clean is Wajib, and if it falls into an unclean place, it must be taken out immediately and washed with water, even if costs to do so. If it is not possible to take it out, for example if it has fallen in a toilet, the Wajib precaution is that toilet must not be used until it is certain it (Torbah) has been dissolved in water.
Source: PERSIAN SHAFAQNA