Drink spilt in seat (6)
I believe the answer is:
tisane
'drink' is the definition.
(tisane is a kind of drink)
'spilt in seat' is the wordplay.
'spilt' is an anagram indicator.
'in'+'seat'='inseat'
'inseat' is an anagram of 'TISANE'.
(Other definitions for tisane that I've seen before include "Herb-tea" , "Herbal tea drink" , "Herbal infusion" , "Infusion of e.g. dried or fresh flowers or leaves" , "relaxing drink" .)