What is the proper way to dispose of water used to clean Altar clothes?
Unless altar cloths have been stained with the Precious Blood they can be laundered in the manner any cloth would be cleaned. Respect for the sacred nature of altar cloths would, however, call for them to be laundered separately from other cloths.
If an altar cloth has been stained with the Precious Blood the stain should first be treated in a sacrarium or failing that in some kind of container with which the water can be poured directly into the ground rather than a drain. After it has been appropriately rinsed it can then be laundered in a usual manner.
Diocese of Fort Wayne South Bend The Proper Care and Cleansing of Altar Linens & Sacred Vessels