Pipe potato, briefly? (4)
I believe the answer is:
tube
'pipe' is the definition.
(I know that pipe can be written as tube)
'potato briefly?' is the wordplay.
'potato' becomes 'tuber' (potato is an example of a tuber).
'briefly?' means to remove the last letter (I've seen 'briefly' mean this).
'tuber' with its final letter taken away is 'TUBE'.
(Other definitions for tube that I've seen before include "Can of beer (colloquial)" , "Pipe - railway" , "Cylindrical hollow conduit" , "Hollow cylindrical object" , "TV" .)