Green’s Dictionary of Slang

bagpipe n.¹

the penis.

1612		Passenger of Benvenuto 569: For little pleasure [he] suffers great paine, that lets his Bagpipe out vpon credite [N].
c.1640		‘North Country Lass’ in Ebsworth Roxburghe Ballads (1897) VIII 88: And then he pluckt his bag-pipes forth, and plai’d melodiously.
1641		J. Johnson Academy of Love 88: The Bag-pipe [...] is a wind instrument, and never playes but when the bag is full.
1660		Mercurius Fumigosus 8 61: [A shepherd] reprehended two maids a milking a Bull, [...] knowing himself better able to administer Musick to the delight of the Milk-maids, with the Bag-pipes in his Breeches.
c.1707		‘Blowzabella’ in Farmer Merry Songs and Ballads (1897) IV 77: Squeakham, Squeakham, Bag-pipe will make ’em / Whisking, Frisking.
1790		‘Bumper Allnight. Esquire’ Honest Fellow 24: So Jockey with haste pull’d out of its case / His merry bagpipe, and play’d with a grace.