Green’s Dictionary of Slang

verbal or written nonsense.

1870		Sportsman (London) 2 Feb.2/1: But what about the writer of the wash in question, ought not to ashamed of himself too.
1913		A. Lunn Harrovians 287: ‘You are my trusty Praetors [...] I depend on my Sixth to be true to their responsibilities.’ You know the kind of wash.
1927		(con. 1918) J.W. Thomason Red Pants 77: Well, anyway, you didn’t give me any wash about wantin’ to be a sister to me.