Large piece of infrastructure, clean, mostly constructed from the rear (6,3)
I believe the answer is:
hoover dam
'large piece of infrastructure' is the definition.
I can't tell whether this definition defines the answer.
'clean mostly constructed from the rear' is the wordplay.
'clean' becomes 'hoover' (hoovering is a kind of cleaning).
'mostly' means to remove the last letter (most but not all of the word).
'constructed' becomes 'made' ('make' can be a synonym of 'construct').
'from the rear' says the letters should be written backwards.
'made' with its final letter taken off is 'mad'.
'mad' backwards is 'dam'.
'hoover'+'dam'='HOOVER DAM'
Can you help me to learn more?
(Other definitions for hoover dam that I've seen before include "feat of US engineering" , "liquid restraint" , "Barrier on Colorado river" , "Construction across the Colorado River in Nevada" .)