Catholic Encyclopedia (1913)/Piscina
(Lat. from piscis, a fish, fish-pond, pool or basin, called also sacrarium, thalassicon, or fenestella)
The name was used to denote a baptismal font or the cistern into which the water flowed from the head of the person baptized; or an excavation, some two or three feet deep and about one foot wide, covered with a stone slab, to receive the water from the washing of the priest's hands, the water used for washing the palls, purifiers, and corporals, the bread crumbs, cotton, etc. used after sacred unctions, and for the ashes of sacred things no longer fit for use. It was constructed near the altar, at the south wall of the sanctuary, in the sacristy, or some other suitable place. It is found also in the form of a small column or niche of stone or metal.
ROCK, Church of Our Fathers, IV (London, 1904), 194; BINTERIM, Denkwürdigkeiten, IV, 1, 112: Theol. prakt. Quartalschrift (1876), 33.