Bottle setter consumed in the flipping toilet (4)
I believe the answer is:
vial
'bottle' is the definition.
(vial is a kind of bottle)
'setter consumed in the flipping toilet' is the wordplay.
'setter' becomes 'i' (the person that set the crossword).
'consumed in' indicates putting letters inside.
'the flipping' says the letters should be written backwards.
'toilet' becomes 'lav' ('lav' can be a synonym of 'toilet').
'lav' back-to-front is 'val'.
'i' put into 'val' is 'VIAL'.
(Other definitions for vial that I've seen before include "Small glass container" , "Small container for liquid medicine" , "Small container for liquids" , "Ampoule" , "Small bottle used for medicines, laboratory work, etc" .)