Green’s Dictionary of Slang

you understand? also as v.

1859, 1860		Hotten Dict. of Modern Sl. etc.
1873		Sl. Dict.
a.1909		press cutting in J. Ware Passing Eng. of the Victorian Era 119/1: Whenever you see a chap after your judy, the best thing to do is to go up to her and tell her that you don’t mean to stand her blooming kid, that you dry land her emag.
1935		A.J. Pollock Und. Speaks 34/2: Dry land, you, understand.