The Collaborative International Dictionary of English v.0.48:
Back \Back\, n. [F. bac: cf. Arm. bag, bak a bark, D. bak tray,
1. A large shallow vat; a cistern, tub, or trough, used by
brewers, distillers, dyers, picklers, gluemakers, and
others, for mixing or cooling wort, holding water, hot
Hop back, Jack back, the cistern which receives the
infusion of malt and hops from the copper.
Wash back, a vat in which distillers ferment the wort to
Water back, a cistern to hold a supply of water; esp. a
small cistern at the back of a stove, or a group of pipes
set in the fire box of a stove or furnace, through which
water circulates and is heated.
2. A ferryboat. See Bac, 1.