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1.
Tapping up is the attempt to crack onto somebody, not necesarily involving intercourse, maybe just a cheeky pull. It can also can be used in the context of failure.
"Tim tried to tap up that girl last night but failed"
by Hertford College May 15, 2008
 
2.
An English slang word word meaning a bribe
"If you need to get your motor through it's MOT just tap up Bill and he will sort you out"
by Darrenwl February 07, 2007