Description of rubbish stock mostly offered in bargain? (8)

'description of rubbish' is the definition.

'stock mostly offered in bargain?' is the wordplay.
'stock' becomes 'trite' (I've seen this before).
'mostly' means to remove the last letter.
'offered in' is an insertion indicator.
'bargain?' becomes 'deal' ('deal' can be a synonym of 'bargain').
'trite' with its last letter removed is 'trit'.
'trit' inserted within 'deal' is 'DETRITAL'.