Journey about in empty tank (4)
I believe the answer is:
trek
'journey' is the definition.
(trek is a kind of journey)
'about in empty tank' is the wordplay.
'about' becomes 're' (regarding**).
'in' indicates putting letters inside.
'empty' says to hollow out the word (remove centre letters).
'tank' with its middle removed is 'tk'.
're' going inside 'tk' is 'TREK'.
(Other definitions for trek that I've seen before include "Long hard journey on foot" , "A long arduous walk" , "Slog" , "Long walk, expedition" , "Extended journey" .)