Freely available, like H or C (2,3)
I believe the answer is:
on tap
'freely available' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for on tap that I've seen before include "where C or H is seen?" , "Readily available" , "Immediately available like beer in pub" , "Ready for immediate use" , "Always available" .)