Beer glass preferably filled by taps (8)
I believe the answer is:
schooner
'beer glass' is the definition.
(I've seen this in another clue)
'preferably filled by taps' is the wordplay.
'preferably' becomes 'sooner' (eg 'I'd sooner sit' means 'I would prefer to sit').
'filled by' means one lot of letters goes inside another.
'taps' becomes 'ch' (cold and hot taps).
'sooner' going around 'ch' is 'SCHOONER'.
(Other definitions for schooner that I've seen before include "Two-masted sailing ship" , "Old sailing ship and tall sherry glass" , "Large beer or sherry glass" , "Two-master; a glass" , "A measure or glass for sherry" .)