Every bit invested in liquid — there's money in it (6)
I believe the answer is:
wallet
'there's money in it' is the definition.
(a wallet contains money)
'every bit invested in liquid' is the wordplay.
'every bit' becomes 'all' (all of it).
'invested in' means one lot of letters goes inside another.
'liquid' becomes 'wet' (wet means watery or liquid).
'all' inserted into 'wet' is 'WALLET'.
(Other definitions for wallet that I've seen before include "Small flat money case" , "Billfold (US)" , "Money holder" , "ready to come out of it?" , "Money-holder" .)