on tap

From tap. Sense 2 recorded from 1483.

on tap

1. (of beer, etc.) Available directly from the barrel by way of a tap.
   • 2011, Todd Keith, Insiders' Guide® to Birmingham‎^[1]:

     All three locations each offer at least 50 different draft beer choices ranging from popular beers from major brewers to exclusive microbrews not usually available on tap.

2. (by extension) Readily available; ready for use in whatever quantity is desired.
3. On an agenda, planned, expected.

• Paton, panto, panto-