Green’s Dictionary of Slang

to wash down or off with water.

c.1566		Harman Caveat for Common Cursetours in Viles & Furnivall (1907) 85: I saye by the Salomon I will lage it of [sic] with a gage of benebouse [...] I sweare by the masse I will washe it of with a quart of good drynke.
1608		Dekker Belman of London (3rd) J3: [as cit. c.1566].