Green’s Dictionary of Slang

bill on the pump at Aldgate n.

also Aldgate pump, draught on the pump at Aldgate
[proper name Aldgate Pump, near junction of Fenchurch Street and Leadenhall Street in London; the pump was a City institution, but hardly a safe financial one]

a bad bill of exchange.

[UK]Grose Classical Dict. of the Vulgar Tongue n.p.: draught, or bill, on the pump at aldgate. A bad or false bill of exchange.
[UK]Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Algate. a draught on the Pump at Algate. a Bad bill of Exchange, drawn on persons that have no Effects of the ‘Drawer’. a play on the Word Draught.
[UK]Lex. Balatronicum.
[UK]Egan Grose’s Classical Dict. of the Vulgar Tongue.
[UK]W.T. Moncrieff Scamps of London II i: bob: I have sent him for a draft I’ve drawn on my banker. charl.: Aldgate pump!
[UK]Pembs. Herald (Wales) 8 May 4/3: The slang dealer likes wrapping up his meaning in a joke for his customer to unwrap, generally finding something unpleasant inside. You want your money back from him, and he offers a ‘draught’ on Aldgate pump; you confess yourself a fool for trusting him, and he blandly recommends you to go to Battersea (famous for its herb gardens) to have your ‘simples’ cut.