Glances up, drains third of stout, cheers! (4)
I believe the answer is:
skol
'stout cheers' is the definition.
'skol' can be an answer for 'cheers' (Scandinavian term for 'cheers' when drinking). I am not sure about the 'stout' bit.
'glances up drains third' is the wordplay.
'glances' becomes 'ks' (I can't justify this - if you can you should give a lot more credence to this answer).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'drains' suggests removing the centre (I've seen 'drained' mean this).
'third' becomes 'ordinal' (similar in meaning).
'ordinal' with its centre taken out is 'ol'.
'ks' backwards is 'sk'.
'sk'+'ol'='SKOL'
'of' is the link.
Can you help me to learn more?
(Other definitions for skol that I've seen before include "Scand. drinking toast" , "(Scandinavian) "bottoms up"" , "Scandinavian toast" , "Cheers in Copenhagen" , "your health!" .)