Used pants seen in river for period of time (7)
I believe the answer is:
tuesday
'period of time' is the definition.
(Tuesday is an example)
'used pants seen in river' is the wordplay.
'pants' indicates anagramming the letters (UK informal term for 'nonsense' or 'rubbish').
'seen in' means one lot of letters goes inside another.
'river' becomes 'tay' (River Tay).
'used' anagrammed gives 'uesd'.
'uesd' inserted within 'tay' is 'TUESDAY'.
'for' is the link.
(Other definitions for tuesday that I've seen before include "Day for sea duty?" , "Ruby - (The Rolling Stones)" , "24-hour period" , "Shrove ____" , "See 1 down" .)