Place to keep one good plug (6)
I believe the answer is:
Here is my best explanation:
'plug' is the definition.
(spigot is a kind of plug)
'place to keep one good' is the subsidiary indication.
'place' becomes 'spot' ('spot' can be a synonym of 'place'**).
'to keep' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'good' becomes 'g' (abbreviation).
'spot' placed around 'ig' is 'spigot'.
(Other definitions for spigot that I've seen before include "Plug for a cask's vent hole", "Cask's plug", "Peg to control the flow of a tap", "Peg that stops the vent of a cask", "Device for stopping", "Peg to seal vent in cask", "Tap fitted to a cask", "Tap, faucet", "Pigs to vent-peg" and "Small peg or plug".)