Dispenser of liquid sulphur supported by petition (7)
I believe the answer is:
sprayer
'dispenser of liquid' is the definition.
'sulphur supported by petition' is the wordplay.
'sulphur' becomes 's' ('S' can be a synonym of 'sulphur').
'supported by' is a charade indicator (letters next to each other) (letters go below - in down clue).
'petition' becomes 'prayer' ('prayer' can be a synonym of 'petition').
's'+'prayer'='SPRAYER'
(Other definitions for sprayer that I've seen before include "One dispensing deodorant" , "Sprinkler" , "Perhaps Mister" , "Dispersing agent - aerosol" , "he'll paint your car" .)