Green’s Dictionary of Slang

custom house n.

the vagina.

a.1680		Rochester (1680) ‘On Rome’s Pardons’ in Works (1999) 247: Did Christ e’er keep a Custom-House for Sin?
1768		Gentleman’s Bottle-Companion 16: Here’s [...] Eve’s custom-house where Adam made his first entry.
1772		G. Stevens ‘The Sentiment Song’ in Songs Comic and Satyrical 126: [as cit. 1768].
1837		‘The Chapter of Smutty Toasts’ in Icky-Wickey Songster 9: [as cit. 1768].
1890–1904		Farmer & Henley Sl. and Its Analogues.

SE in slang uses

In compounds

custom house goods (n.) [‘the stock in trade of a prostitute, because fairly entered’ (Grose, 1796)]

the vagina.

[1739		Joe Miller’s Jests No. 3: Mr. H---rr---n, one of the Commissioners of the Revenue in Ireland, being [...] at the Play-House in Dublin, Monoca Gall, the Orange Girl, [...] striding over his Back, he popp’d his Hands under her Petticoats: nay, Mr. Commissioner, said she, you’ll find no Goods there but what have been fairly entered].
c.1786		Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Custom House Goods The Whores Stock in Trade because they have been duly entered.
1788, 1796		Grose Classical Dict. of the Vulgar Tongue (2nd, 3rd edn) n.p.: Custom-house Goods. The stock in trade of a prostitute, because fairly entered.
[1790		Banquet of Wit 23: as 1739].
1811		Lex. Balatronicum.
1823		Egan Grose’s Classical Dict. of the Vulgar Tongue.
c.1850		Peeping Tom (London) 2 8/2: The commissioner in revenue [...] popped his hand under her petticoats. ‘Nay, commissioner,’ said she,‘ you’ll find no goods there but what have been fairly entered’.
1890–1904		Farmer & Henley Sl. and Its Analogues.

custom house officer (n.) [pun on permitting ‘goods’ to ‘pass through’]

a laxative pill.

1860		Hotten Dict. of Modern Sl. etc. (2nd edn).
1864, 1867, 1870		Hotten Sl. Dict.
1873		Sl. Dict.