Mary Ann

Having listened to Mulligan's clowning about old Mother Grogan making water, Stephen hypothesizes that she "was, one imagines, a kinswoman of Mary Ann." Mulligan picks up on the allusion and is soon belting out a song that he and Stephen both know:

For old Mary Ann
She doesn’t care a damn,
But, hising up her petticoats...

Slote notes that "hising," according to the OED, means "to lift, especially to raise a sail." Given the lifting of skirts, and the link with Mother Grogan, the omitted line must have something to do with urination.

John Hunt 2011

Source: xpedition.be.

Source: waterqualitynz.info.