Contraption of pipes emptied over grain regularly (5)
I believe the answer is:
organ
'contraption of pipes' is the definition.
'organ' can be an answer for 'pipes' ('organ pipe' can be a synonym of 'pipe'). I am unsure of the 'contraption of' bit.
'emptied over grain regularly' is the wordplay.
'emptied' says to hollow out the word (remove centre letters).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'over' with its centre taken out is 'or'.
The alternating letters of 'grain' are 'gan'.
'or'+'gan'='ORGAN'
Can you help me to learn more?
(Other definitions for organ that I've seen before include "Eg, heart, liver" , "music producer" , "Large musical instrument often heard in church" , "Medium of information - most churches have one" , "What makes use of full stops" .)