Green’s Dictionary of Slang

plug-tail n.

the penis.

1701		N. Ward ‘A Walk to Islington’ in Writings (1704) 65: Desirous of Trading with some Interloper, / Disdaining old Plug-tail, unfit for a Stopper.
1733		Laugh and Be Fat 20: Lug out your Smock-smelling Plugtail, that I may see your Condition.
1785, 1788, 1796		Grose Classical Dict. of the Vulgar Tongue.
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
1890–1904		Farmer & Henley Sl. and Its Analogues.