It carries waste when describing tight trousers (9)
I believe the answer is:
drainpipe
This clue could be a double definition.
'it carries waste when' is the first definition.
The definition suggests a singular noun which matches the answer.
'tight trousers' is the second definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'describing' acts as a link.
Can you help me to learn more?
(Other definitions for drainpipe that I've seen before include "Sort of bags" , "water-carrier" , "Waste outlet" , "sort of trouser" , "Waste water carrier" .)