Cesspool
late 17th century (denoting a trap under a drain to catch solids): probably an alteration, influenced by pool1, of archaic suspiral ‘vent, water pipe, settling tank’, from Old French souspirail ‘air hole’, based on Latin sub- ‘from below’ + spirare ‘breathe’.
wiktionary
From earlier sesspool. Origin uncertain.
Possibly an alteration of English dialectal suspool, from suss, soss(“puddle; mire”) + pool. Alternatively, from a folk etymology (influence from pool) from earlier cesperalle, alteration of Middle English suspiral, from Middle French souspirail(“air hole”), from soupirer, souspirer(“to sigh, breathe”), from Latin suspirare.
etymonline
cesspool (n.)
also cess-pool, "cistern or well to receive sediment or filth," 1670s, the first element perhaps an alteration of cistern, or perhaps a shortened form of recess [Klein]; or the whole may be an alteration of suspiral (c. 1400), "drainpipe," from Old French sospiral "a vent, air hole," from sospirer "breathe," from Latin suspirare "breathe deep" [Barnhart]. Meaning extended to "tank at the end of the pipe," which would account for a possible folk-etymology change in final syllable.
Other possible etymologies: Italian cesso "privy" [OED], from Latin secessus "place of retirement" (in Late Latin "privy, drain"); dialectal suspool, from suss, soss "puddle;" or cess "a bog on the banks of a tidal river."
