Tap one of those in 19 down similarly (4)
I believe the answer is:
milk
'tap' is the definition.
(milking is a kind of tapping)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for milk that I've seen before include "Dairy product" , "Extract money from" , "A white drink" , "Use" , "Exploit" .)