Rubbish bin initially dumped in filling station (7)
I believe the answer is:
garbage
'rubbish' is the definition.
(thesaurus)
'bin initially dumped in filling station' is the wordplay.
'initially' says to take the initial letters.
'dumped in' means one lot of letters goes inside another.
'filling station' becomes 'garage'.
The first letter of 'bin' is 'b'.
'b' going into 'garage' is 'GARBAGE'.
(Other definitions for garbage that I've seen before include "Refuse - worthless talk" , "Litter" , "Refuse - tripe" , "Pop group; rubbish" , "Food waste or trash" .)