"Thou shalt wash me, O Lord". These words, familiar to the laity from the Ceremony which precedes Sunday Mass, come from Psalm 50 (51) , which, in the more penitential parts of the year, comes first in Lauds. So your clergy are currently saying this psalm daily.
I thought, since this blog is nothing if not strictly Ecumenical, you might find helpful to have some presbyterian input. Notice that the writer, unlike most modern Catholics, is not afraid to conclude with a sound piece of Typology.
"Hyssop is an herb generally known, and in Hebrew called esob. It was commonly made use of in purification instead of a sprinkler: thus God commanded the Hebrews, when they came out of Egypt, to take a bunch of hyssop, to dip it in the blood of the Paschal Lamb, and sprinkle the lintel and the two side-posts with it. Sometimes they added a little wool to it, of a scarlet colour. So in the purification of lepers, they dipped a bunch composed of hyssop, the branches of cedar, and red wool, in water, mingled with the blood of a bird, and with it sprinkled the leper.
"David alludes to these ceremonial purifications: Purge me with hyssop and I shall be clean: that is, 'As lepers and other unclean persons are by thy appointment purified by the use of hyssop and other things, so do thou cleanse me, a most leprous and polluted creature, by thy grace, and by the virtue of the Blood of Christ, which is represented and signified by those ceremonial usages.'"
The Presbyterian Alexander Cruden, A Complete Concordance, 1737.