From; The Ecclesiastical Dictionary 1900 A.D.
"Piscina (Sacrarium) In liturgy a term applied to a walled-up cavity of a certain depth, covered with a round or oval stone, which is pierced through the middle. THere should be at least one piscina in each church as a receptacle for the water that has served, either for baptism, or to cleanse the sacred vessels and linen. It is also used as a depositary for the ashes of altar ornaments and linens, and other blessed things which should be burned when they can no longer be used. The piscina also serves the purpose of receiving holy water taken from the holy water-basin or font, and, in general, for all articles used in the sacred service of divine worship, in order that they may not be exposed to profanation."
From : A Handbook for the Sacristan 1932 A.D.
"The Sacrarium. This is a basin used to wash and clean the chalice, ciborium or other sacred vessels, and also the small linens used in direct connection with the sacred vessels or certain ceremonies. Here it is also that the priest washes his hands
after certain ceremonies. It has a drain pipe which connects with the ground, so that such water may flow into the earth"
Only the priest, deacon or acolyte should be using the sacrarium.
On March 19 2004 A.D. Pope JPII issued a stern directive which was to be implimented IMMEDIATELY of all things pertaining to the Eucharist and Chapter V item 119 & 120 deals with the priest prewashing the corporal etc before it is given to the women to be laundered. And it was promptly ignored as too traditional.
http://www.vatican.va/roman_curia/congregations/ccdds/docuмents/rc_con_ccdds_doc_20040423_redemptionis-sacramentum_en.html
I don't believe sacrariums were built so much for convenience but for safety; keeping sacred things in close proximity to avoid abuses.