Flower attached to tail of giant guinea pig (6)
I believe the answer is:
taster
'guinea pig' is the definition.
(somebody who tastes or tests a new product)
'flower attached to tail of giant' is the wordplay.
'flower' becomes 'aster' (type of flower).
'attached to' says to put letters next to each other.
'tail of giant' becomes 't' (I can't explain this - if you can you should give a lot more credence to this answer).
'aster' put after 't' is 'TASTER'.
(Other definitions for taster that I've seen before include "Art set (anag.)" , "A sample to try" , "One samples" , "Sample intended to stimulate interest" , "Winery worker" .)