In the celebration of mass, the corporal and the purificator are the two pieces of linen that make the most direct contact with the eucharistic species. When these linens are to be cleaned, often there are crumbs or particles of the Body as well as drops of the Blood on the linens.
A long held tradition of cleaning such linens is to first soak them in warm water until the particles and stains are all dissolved. Often soap and colour bleach may be added to ensure there is no more eucharistic species remaining on the linens themselves. The water is then poured into the ground, for watering plants or down the special sacrarium built in to the sacristy that goes into the ground.
If the linens are then sufficiently void of particles and stains, they may be washed in the normal fashion. However, one may add the extra precaution of washing it by hands so the water may be poured into the ground instead of going into the sewage. I even know one religious house that has a dedicated washing machine designed to have the used water go directly into the ground.