Ultimately vacuous glib talk in splash (7)
I believe the answer is:
spatter
'splash' is the definition.
('spatter' can be a synonym of 'splash')
'ultimately vacuous glib talk' is the wordplay.
'ultimately' says to take the final letters.
'glib talk' becomes 'patter' (I've seen this before).
The last letter of 'vacuous' is 's'.
's'+'patter'='SPATTER'
'in' acts as a link.
(Other definitions for spatter that I've seen before include "Set part (anag.)" , "Cover with droplets" , "Sprinkle" , "shower" , "spray" .)