tap, n.² — Green’s Dictionary of Slang

tap n.²

1. (US Und.) a person likely to give a donation to a charitable cause.

1928

J. O’Connor Broadway Racketeers 93: The Taps considered easy to land are known as ‘Push-Overs.’.

2. (US tramp) a house known to be a good place to beg.

1937

J. Worby Other Half 105: I whiled away the time swapping yarns and getting information about the good ‘taps’ in the next town.

3. a loan; an act of requesting a loan.

1995

J. Stahl Permanent Midnight 343: A guy who was clearly crazy or working me for a tap.

turn on the tap (v.) [note also tap v.² (1a)]

in prize-fighting, for a nose to bleed; to cause a nose to bleed.

1853		N.Y. Clipper n.p.: Donnelly came up with the tap turned on from his left brow .
1857		Bell’s Life in Victoria (Melbourne) 5 Sept. 3/1: Sayers returned very heavily on the snorer, once more turning on the tap.
1860		Bell’s Life in Sydney 7 Apr. 4/1: He napped a hot ’n on the sneezer which instantly turned on the tap [...] In awkward exchanges the tap was turned on again from a cut on Dan’s cheek.
1860		Glasgow Herald 20 Apr. 4/3: Tom got a hot ’un on the whistler, which shook his ivories and turned on a fresh tap.