Green’s Dictionary of Slang

to defecate, to excrete.

1612		J. Taylor Laugh and Be Fat 30: Most men say thou pissest inke; / If it be true, I’de giue my guilded raper, / That to thy inke thou couldst sir-reuerance paper.
1652		Mercurius Democritus 7–14 Apr. 10: This Monster surreverences out all the monsterous Lies that come abroad.
c.1850		Peeping Tom (London) 30 120/2: One night [...] she sir-reverenced in his place [i.e. side of the bed].