The Mendai and Elcesaite entries both point here: a Jewish sect of daily washing that Adams links to the Christians of St John, part of the baptist milieu the archive tracks toward Mani.
In Hannah Adams
In Adams’s own words, from the 1817 Dictionary. Each passage is quoted verbatim under its own entry.
HEMERO-BAPTISTS, a Jewish sect which practised daily baptism, or frequent religious washings; which is said to have been the case also with the Christians of St. John, at least 011 some occasions.||
Hannah Adams, A Dictionary of All Religions and Religious Denominations, 4th ed. (Boston: Cummings and Hilliard, 1817), entry “Hemero-Baptists” (p. 105).