VAT? It’s cost you job, last of all (3)
I believe the answer is:
tub
'vat?' is the definition.
('tub' can be a synonym of 'vat')
'cost you job last of all' is the wordplay.
'last of all' suggests the final letters.
The last letters of 'cost you job' are 'TUB'.
'it's' is the link.
(Other definitions for tub that I've seen before include "Large open container" , "Slow boat; box of ice-cream" , "Pot (of e.g. ice-cream)" , "Pot, vat" , "Container for yogurt, ice-cream" .)