Binge before opening oxygen tank (7)
I believe the answer is:
overeat
'binge' is the definition.
(synonyms)
'before opening oxygen tank' is the wordplay.
'before' becomes 'ere' (poetic term for 'before').
'opening' is an insertion indicator (some letters open a gap in others).
'oxygen' becomes 'O' (atomic symbol for oxygen).
'tank' becomes 'vat' (I've seen this before).
'o'+'vat'='ovat'
'ere' placed inside 'ovat' is 'OVEREAT'.
(Other definitions for overeat that I've seen before include "Take too much food" , "Consume too much like a glutton" , "Be greedy" , "Stuff oneself silly" , "Consume excessively" .)