To access some large, abundant, or powerful resource. The man was found guilty for illegally tapping into the city's electrical grid without paying.The new film taps into the nostalgia of fans who grew up with the franchise when they were kids.
tap something into something
and tap something in
to move something in with light blows. The mechanic tapped the bracket into place. The worker tapped in the bracket.
tap into
v.
1. To gain access to some resource: The building tapped into the city's water supply.
2. To take advantage of some sentiment: The politician tapped into voter anger and won the election.