Fat, everyone aboard tug (6)
I believe the answer is:
tallow
'fat' is the definition.
(fat used to make candles)
'everyone aboard tug' is the wordplay.
'everyone' becomes 'all' (all people).
'aboard' is an insertion indicator.
'tug' becomes 'tow' (I've seen this before).
'all' inserted inside 'tow' is 'TALLOW'.
(Other definitions for tallow that I've seen before include "Animal fat used to make ..." , "Rendered fat used for making candles" , "Candle wax" , "burning fat" , "Melted, clarified animal fat" .)