Heavy food dogs eat, not a liquid (6)
I believe the answer is:
stodge
'heavy food' is the definition.
(I've seen this before)
'dogs eat not a liquid' is the wordplay.
'not' is a deletion indicator.
'liquid' indicates an anagram.
'dogs'+'eat'='dogseat'
'dogseat' with 'a' taken away is 'dogset'.
'dogset' is an anagram of 'STODGE'.
(Other definitions for stodge that I've seen before include "Heavy filling food" , "Steamed pudding" , "Sticky stuff" , "Food that's hard to digest" , "Heavy solid food" .)