Bums are on view from behind in eg cossies (7)
I believe the answer is:
toerags
'bums' is the definition.
(I've seen this before)
'are on view from behind in eg cossies' is the wordplay.
'on view from behind' says the letters should be written backwards.
'in' means one lot of letters goes inside another.
'eg cossies' becomes 'togs' (informal term for clothing).
'are' written backwards gives 'era'.
'era' inserted inside 'togs' is 'TOERAGS'.
(Other definitions for toerags that I've seen before include "Bums" , "Unpleasant people" , "Wretched folk" .)